Quantum Chemical Study on HKrC5N, HXeC5N, and Related Rare

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Article 5

A Quantum Chemical Study on H-Kr-CN, HXe-CN, and Related Rare Gas Compounds 5

Michal Turowski J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/jp509837p • Publication Date (Web): 23 Dec 2014 Downloaded from http://pubs.acs.org on January 17, 2015

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A Quantum Chemical Study on H-Kr-C5N, H-Xe-C5N, and Related Rare Gas Compounds

Journal:


Manuscript ID:

jp-2014-09837p.R1

Manuscript Type:

Special Issue Article

Date Submitted by the Author: Complete List of Authors:

20-Dec-2014 Gronowski, Marcin; Institiute of Physical Chemistry, Turowski, Michal; Institiute of Physical Chemistry, Kolos, Robert; Institute of Physical Chemistry, Astrochemistry Group

ACS Paragon Plus Environment

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A Quantum Chemical Study on HKrC5N, HXeC5N, and Related Rare Gas Compounds. Marcin Gronowski, Michał Turowski*, and Robert Kołos Institute of Physical Chemistry of the Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland Abstract The recent identification of HRgC5N (Rg=Kr, Xe) in a cryogenic matrix calls for an in-depth theoretical study on these compounds. Here we present the results of CCSD(T), MP2, and DFT calculations concerning the molecular structure, stability and vibrational spectroscopy. The procedure combining CCSD(T) calculations for variable H-Rg distances with the anharmonic description of the corresponding stretching vibration, based on a Morse-type potential energy function, was proposed, and has led to a good agreement between computational and experimental values for H-Rg stretching frequencies, at relatively low computational costs. High Raman scattering activity of HRgC5N and of its isomers, predicted at the DFT level, gives some prospects for the detection of these molecules with a method alternative to the IR absorption spectroscopy. Keywords: rare gas compounds, vibrational spectroscopy, stability, cyanopolyynes, DFT, coupled clusters. * Corresponding author. Tel.: +48 22 3433353; fax: +48 22 3433333. E-mail address: [email protected].



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1. Introduction Solid rare gas (Rg) matrixes offer a convenient environment for the synthesis and isolation of HRgR hydrides, where R stands for an unsaturated acetylenic1–4 or cyano group-containing5–9 moiety. Recently, we have reported on the identification of the largest members of this group, namely HKrC5N and HXeC5N.9 All laboratory identifications of such ‘inclusion species’ were accomplished with IR absorption spectroscopy supported with quantum chemical calculations. The typical synthetic procedures applied for HRgCnN species (n=1, 3, 5) involved the UV-laser photolysis of certain precursor molecules embedded within a rare gas matrix (Kr or Xe), followed with a gentle temperature warm-up (thermal annealing) of the sample. The creation of HXeC3N (from HC3N) and of HRgC5N (from HC5N, Rg=Kr, Xe) was also observed after the solidification of appropriate gas mixtures subjected to electric discharges.9 Analogous argon derivatives, while theoretically possible,8–10 have never been observed. The formation mechanism possibly involves the photochemical H-C bond cleavage, the temperature-induced increase of hydrogen atoms mobility, and eventually the recombination of atoms with other photofragments. The creation of HRgCnN may also involve some matrix rearrangement. Hydrides belonging to this family usually feature a H-Rg-C structural motif; HXeNC 5 and HXeNCO are the only molecules for which the H-Rg-N bonding was observed. The rare gas atom is in HRgCnN rather weakly bound to carbon; the relevant part of the potential energy surface (PES) has a relatively shallow minimum. Therefore, the reliable theoretical prediction of vibrational frequencies is difficult. In addition to that, an especially high anharmonicity was postulated for the H-Rg stretching vibration in several inclusion species. 8,11–13


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Computational results concerning the thermodynamic stability and dissociation channels have been reported e.g. for the rare gas compounds HRgF and HXeC2H.14–19 One of the dissociation routes, referred to as B2 (“two-body”) channel, has been predicted for HArF,14 HKrF,14,15 and HXeC2H

17,18

at the MP2 and CASPT2 levels of theory. It involves a H-Rg-R

bending mode (R standing for the remaining part of the molecule), and leads to the decomposition of HRgR into Rg and HR. The reaction, always exothermic,16 proceeds via a transition state; the relevant energy barrier has been estimated as 2 eV for HXeC2H.17,18 Conversely, the B3 (“three body”) channel is associated to the H-Rg stretching mode, and results in the production of separated H, Xe and R fragments. It is typically slightly endothermic, but the energy barrier is usually predicted as smaller than in the B2 case (e.g., only 1 eV for HXeC2H).17 For HRgR species in cryogenic media, B3 is therefore expected to be the main decomposition route.16 Here we present the results of a coupled cluster theoretical approach to geometry and vibrational spectroscopy of HRgC5N molecules. This is the extension of former9 DFT and MP2 studies. We discuss, based on DFT predictions, the prospects for possible IR or Raman spectroscopic detection of related isomeric species. We also check if the results of DFT calculations are consistent with experimental data concerning the energetics, and in particular the photochemical stability of these compounds.



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2. Computational methods Molecular structure, vibrational frequencies, IR absorption intensities, and Raman activities were computed using either the Gaussian 0320 or Gaussian 0921 suit of programs. For HRgC5N (Rg=Ar, Kr, Xe), the coupled cluster method, featuring the iterative treatment of single and double excitations and the perturbative treatment of triple excitations (CCSD(T)),22 was used to determine the molecular geometry. The electron density distribution was predicted by means of the Natural Bond Orbital (NBO) analysis.23 Density functional theory (DFT) calculations with the Becke 3-term correlation functional and the exchange functional introduced by Lee, Yang, and Parr (B3LYP),24 were carried out to obtain Raman scattering activity values for vibrational transitions. To calculate the vibrational frequencies (in particular that of the H-Rg stretching), a number of other DFT functionals have also been tested. In several instances, the 2nd order Møller–Plesset perturbation theory (MP2)25,26 was applied. Anharmonic frequencies were calculated via the 2nd order perturbative anharmonic analysis (VPT2).27 The augmented triple-zeta Dunning-type basis set with pseudopotentials (aug-cc-pVTZ-PP)28 was chosen for the calculations for Kr or Xe atoms, and the aug-ccpVTZ basis set29 in all other cases, unless explicitly stated in the text. The abbreviation X/Y/Z, used throughout this paper, denotes the calculations carried out with a method X, employing the basis set Y in case of all atoms but Kr and Xe, for which the basis set Z was used. Considering the stability of title molecules, we have assumed, as the most likely ones, the following two types of decomposition events occurring in a low temperature crystal environment: (i) the hydrogen detachment and (ii) the isomerisation towards a loose complex formed by a noble gas atom and a C5HN-stoichiometry molecule. The dependence of total molecular energy on the H-Rg distance has been analysed with the relaxed PES scan; the QST3 procedure30,31 was employed to localize the transition states. The intrinsic reaction


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coordinate (IRC)32,33 calculations allowed for an insight into the reaction paths. It is to be noted that all theoretical results presented here refer to isolated, gas-phase molecules.

3. Results and discussion 3.1 Molecular structures Previously reported9 calculations on HRgC5N have been currently revisited with the coupledcluster approach (Fig. 1). The comparison of CCSD(T)-derived interatomic distances to those obtained via DFT or MP2 calculations shows differences that are usually not exceed 0.04 Å. The largest deviations are observed for the H-Ar bond, where the length calculated with CCSD(T) is by 0.06 Å and by 0.04 Å longer than predicted at MP2 and B3LYP levels, respectively. All three methods lead therefore to qualitatively similar geometries.

Figure 1. Interatomic distances (in Å, bottom) and partial charges (from the B3LYP NBO analysis; in atomic units, top) for HRgC5N molecules (Rg = Ar, Kr, Xe), as derived at the CCSD(T)/aug-cc-pVTZ/aug-cc-pVTZ-PP level of theory.

The Rg-C bond length predicted for HRgCnN molecules (Rg = Ar, Kr, Xe; n = 1, 3, 5) was found to slightly decrease with n (Fig. 2, bottom). The influence of the size of the CnN group on H-Rg bond length is much smaller (Fig. 2, top), especially in the case of H-Ar, where,



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interestingly, a small decrease (of 0.17 pm) has been predicted for n changing from 1 to 5, in contrast to a slight increase obtained for H-Kr and H-Xe distances. The analysis of charge distribution accomplished at the B3LYP level shows, as anticipated, that Xe acts most strongly, compared to Ar and Kr, in donating the electron density to neighbouring hydrogen and carbon atoms. HXeC5N features also a lower electric dipole moment, calculated as 11.0 D (MP2) or 11.8 D (B3LYP), than Kr- and Ar-bearing molecules: 11.8 D (MP2) or 12.6 D (B3LYP) for HKrC5N, and 15.0 D (MP2) or 12.8 D (B3LYP) for HArC5N.9


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Figure 2. H-Rg and Rg-C bond lengths (pm) as the functions of n for H-Rg-CnN molecules. Results of the CCSD(T)/ )/aug-cc-pVTZ/aug-cc-pVTZ-PP computations.

Analysing the structure of molecules depicted in Fig.1, one can conclude that the overall geometry of the C5N chain and its electronic structure remain essentially not altered upon the change of an attached noble gas atom. The charge separation is clearly seen, with about 0.6 electron missing from the HRg moiety and distributed over the C5N part. This picture is consistent with the former computational studies on HRgCN and HRgNC molecules.34

3.2 H-Rg vibrational frequencies In previous combined experimental/theoretical research on HRgC3N and HRgC5N,8,9 the scaled harmonic DFT approach gave satisfactory results concerning the frequencies of



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fundamental vibrations – with the exception of the crucial H-Rg stretching, the one being in fact best suited for the detection of discussed molecules, due to its outstanding IR absorption intensity. There, anharmonic DFT calculations were found to substantially improve the quality of theoretical predictions. Importantly, DFT correctly indicated the intensity of the HRg stretching band as by far the highest in IR absorption spectra of these molecules. Of note, the n=1

5

and n=3

8

HRgCnN molecules have been experimentally observed, and

could therefore serve as test species, to check for reliability of the presently performed calculations (see Tables 1 and 2). In one of the former studies, Lundell et al.11 reported on H-Rg stretching frequency being overestimated by MP2 calculations. The important role of anharmonicity and of the electron correlation has been noted.5,35 It should also be remarked that evaluating the performance of theoretical approaches is complicated by the unavoidable presence of a low temperature crystal host. For instance, the H-Xe stretching frequency of HXeCN, first measured in solid xenon, shifts by +24 cm-1 and +45 cm-1 when the same compound is isolated in, respectively, krypton and argon matrixes.5 Similarly, for the analogous vibration of HXeC2H, the Xe-to-Kr matrix shift is +33 cm-1.36 We have presently tested a large collection of computational methods and basis sets to choose the most adequate procedure describing the fundamental H-Rg vibration in HRgCnN. Obviously, the level of theory is critical for the accuracy of the result (Table 1); with the augcc-pVTZ basis set, differences between H-Rg frequency values obtained with different methods can be as high as 550 cm-1. For the analysed mode, method-dependent effects include the following: 1. Harmonic frequencies decrease in the CCD, CCSD, CCSD(T) order;


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2. B3LYP and CCSD yield similar results; 3. CCSD(T)-derived frequencies stand out from those obtained with other methods, being significantly lower; CCSD(T) is also the only method correctly reproducing frequency differences between the investigated HKrCnN and HXeCnN molecules. These results clearly indicate an important influence of electron correlation on the vibrational modes of the HRgC moiety. Large differences between CCSD and CCSD(T) suggest that the static part of correlation energy is important here in the theoretical treatment of vibrational properties. (The importance of static correlation has also been noticed in a Pluta’s et al.37 study on HRgC4H molecules; the static part of correlation energy was however found there to decrease in the Ar, Kr, Xe order.) The results of calculations listed in Table 1 are quite sensitive to the choice of a basis set; collected data suggest CCSD(T)/aug-cc-pVTZ as the recommended level of theory. This is consistent with the results obtained for a neutral HXeH molecule.38 The cost of using the CCSD(T) method with anharmonic treatment of molecular vibrations, for a rather large electronic system - like that of HRgC5N compounds - with an extensive basis set, is high. We have therefore tested an alternative, much less time-consuming procedure described below, which turned out to produce the H-Rg stretching frequencies with a precision similar to that of the regular CCSD(T) approach. The said procedure comprises: 1.

CCSD(T)/aug-cc-pVTZ geometry optimization.

2.

A non-relaxed CCSD(T) potential energy surface scan, leading to energy values for several H-Rg distances.

3.

Fitting a Morse-type potential to energy values obtained in stage 2.



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In what follows it is assumed that anharmonic couplings between H-Rg stretching and other vibrational modes are weak, and that the mode referred to as “H-Rg stretching” is dominated by this particular vibration. The examination of nuclear displacements confirmed the validity of such an assumption; the mode is indeed predominantly localized in the HRg part of the molecule. With regard to stage (2), seven near-equilibrium H-Rg interatomic distances were chosen, differing by a step of 0.0125 Å. As has been checked, the use of twice as many steps, distributed within the same overall distance range, did not noticeably affect the results. The Morse-type potential can be expressed as:

V ( r )= D⋅exp(− α⋅(r− r 0))(exp(− α⋅(r− r 0 ))− 2)+ V ∞

where r denotes the H-Rg distance. The equilibrium bond length r0 and dissociation energy D, together with the parameters V∞ (energy at r=∞) and α (defining the width of the curve), were found via the least squares fitting procedure (stage 3). The results are illustrated by Figs. 3 and 4. Corresponding vibrational energy levels have then been calculated as:

1     hν v +   2   1 Ev = (V∞ − D )+ hν v +  −   2 4⋅ D 

2

where:

ν=

α D π 2⋅ µ


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with h denoting the Planck constant and µ - the reduced mass of an H-Rg oscillator. Ensuing vibrational frequency values, for a number of experimentally observed HRgCnN molecules, are listed in Table 2.

Figure 3. CCSD(T)/aug-cc-pVTZ/aug-cc-pVTZ-PP energy of HKrC5N, as a function of H-Kr distance. Circles indicate calculated values, curves represent the least squares fits with a Morsetype potential (blue) and with a 2nd order polynomial (red dashed line).



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Figure 4. CCSD(T)/aug-cc-pVTZ/aug-cc-pVTZ-PP energy of HXeC5N, as a function of H-Xe distance. Circles indicate calculated values, curves represent the least squares fits with a Morsetype potential (blue) and with a 2nd order polynomial (red dashed line).

While for HKrC5N (Fig. 3), the minimum is slightly (by 0.005 Å) shifted towards larger internuclear distances, for HXeC5N the minimum of Morse potential matches, within 0.001 Å, the equilibrium H-Xe distance obtained with CCSD(T) calculations (Fig. 4). Anharmonic corrections to the H-Kr or H-Xe frequency, resulting from the numbers listed in Table 1, obtained at the DFT level, are confined within the range of ca. -220 to -330 cm-1 for B3LYP and -140 to -330 cm-1 for the APFD functionals (equivalent, on average, to the corrections of -15% and -13%, respectively). For MP2, the analogous differences are -67 to -138 cm-1 (-9% on average). More reliable, however, are the anharmonic corrections provided by the Morse potential-based method. These amount to just -6 to -7% , as can be seen in


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Table 2, and as is depicted by Figs. 3 and 4, in which simple quadratic (i.e. harmonic) functions approximate the calculated potential almost as well as the Morse curve. This is quite similar to what was found for typical C-H, O-H or N-H stretches in allene,39 glicyne,39–41 water,42 formaldehyde,42,43 ethylene, methanol, propyne, or benzene,43 where the calculated anharmonic values were usually by 4 to 8% lower than the harmonic ones. For molecules bearing some structural similarity to presently discussed Kr- and Xe-compounds, namely HMgNC and HMgCN, the anharmonic (VPT2) corrections were, at the CCSD(T) level of theory, approx. -3% for the nitrile and -5% for the isonitrile.44 Anharmonicity of the H-Rg stretching is therefore noticeably exaggerated in the DFT approach. On the other hand, the mean absolute errors of H-Rg frequency predictions (anharmonic), for the molecules listed in Table 1, are 152, 50, and 49 cm-1, respectively, for MP2, APFD, and B3LYP methods, whereas for CCSD(T) computations combined with the Morse-potential procedure (Table 2) the mean error is only 36 cm-1. This demonstrates that the absolute computational accuracy is not directly related to the magnitude of aforementioned anharmonic corrections. Obviously, the appropriate treatment of both electron correlation and anharmonicity is crucial for the meaningful predictions of H-Rg stretching vibration frequencies, as has also been noticed by Huang.45



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Table 1. H-Rg fundamental stretching frequency, as derived with different theoretical methods in harmonic and anharmonic (‘anh.’) approximations. Atomic masses correspond to the most abundant Kr and Xe isotopes (frequency shifts corresponding to other naturally occurring isotopes do not exceed 0.3 cm-1). The basis sets are indicated as Y/Z, where Z stands for the rare gas atom and Y for all remaining atoms.

Method

Experiment

Spieces HKrCN

HXeCN

HKrC3N

HXeC3N

HKrC5N

HXeC5N

1497 a)

1624 a)

1492 b)

1624 b)

1550 c)

1622 c)

aug-cc-pVDZ/aug-cc-pVDZ-PP B3LYP

1793

1786

1830

1797

1829

1794

CAM-B3LYP d)

1999

1882

2002

1876

2001

1871

LC-BLYP e)

2173

1997

2156

1973

2154

1966

MP2

1825

1832

1766

1790

1749

1773

CCD f)

1932

1855

1911

1822

1903

1812

CCSD g)

1779

1787

1772

1764

1765

1755

CCSD(T)

1478

1660

1509

1649

aug-cc-pVTZ/aug-cc-pVTZ-PP APFD h)

1892

1821

1809

1826

1914

1818

APFD anh.

1566

1632

1592

1608

1588

1677

B3LYP

1818

1784

1842

1790

1848

1789

B3LYP anh.

1485

1539

1526

1561

1513

1573

CAM-B3LYP

2004

1871

2000

1866

1998

1862

LC-BLYP

2164

1994

2144

1964

2141

1958

HF

2420

2169

2425

2150

2424

2143


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MP2

1844

1863

1786

1837

1781

1809

MP2 anh.

1727

1768

1648

1736

1645

1742

CCSD

1862

1848

1839

1825

CCSD(T)

1592

1720

1600

1709

aug-cc-pCVTZ i)/aug-cc-pwCVTZ-PP j) MP2

1851 aug-cc-pwCVTZ/aug-cc-pwCVTZ-PP j)

CCSD(T)

1713 def2-SVPD /def2-SVPD k)

B3LYP

1787

1781

1803

1784

1799

1781

CAM-B3LYP

2007

1869

1994

1862

1991

1855

LC-BLYP

2182

1987

2160

1956

2155

1950

MP2

1837

1839

1738

1789

1713

1713

CCD

1934

1868

1884

1834

1867

1824

CCSD

1753

1799

1712

1766

1701

1759

CCSD(T)

1421

1638

1405

1630

a)

Ref. 5

b)

Ref. 8

c)

Ref. 9

d)

Ref. 46

e)

Ref. 47

f)

Ref. 48

g)

Ref. 49–52

h)

Ref. 53

i)

Ref. 54,55

j)

Ref. 56,57

k)

Ref. 58



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Table 2. H-Rg stretching fundamental frequencies, as given by the CCSD(T)-derived Morse potential, compared to the measured values. The aug-cc-pVTZ-PP basis set was applied for rare gases, aug-cc-pVTZ for all remaining atoms.

Species

Experiment CCSD(T)

HKrCN

1497 a)

1443

DKrCN

1109

1064

HXeCN

1624 a)

1612

DXeCN

1178

1167

HKrC3N

1492 b)

1428

DKrC3N

1105

1052

HXeC3N

1624 b)

1602

DXeC3N

1178

1160

HKrC5N

1550 c)

1414

DKrC5N HXeC5N

1042 1622 c)

DXeC5N

1596 1155

HKrC2H

1242 d)

1208

DKrC2D

920

890

HXeC2H

1486 e)

1485

DXeC2D

1078

1075

HKrC4H

1290 f)

1289

DKrC4D

977

950

HXeC4H

1532 f)

1526

DXeC4D

1128

1105

HXeI

1193 g)

1194

DXeI

893

885

HKrC4NC

1367

DKrC4NC

1008

HXeC4NC

1569

DXeC4NC

1136

a) Ref. 5 5; b) Ref. 8 8; c) Ref. 9 9; d) Ref. 7 7; e) Ref. 36 34; f) Ref. 3 3; g) 59


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For

the

Xe

compounds

listed

in

Table

2,

frequencies

estimated

based

on

CCSD(T)/aug-cc-pVTZ-derived Morse functions fit the spectroscopic data fairly well. For Kr derivatives, however, the precision of theoretical predictions tends to decrease with the size of an investigated system. This can be explained by deficiencies in the treatment of electronic correlation (obviously persisting even at the applied coupled-cluster level of theory). The estimated H-Ar frequency for HArC5N is 304 cm–1, which cannot be compared to the experimental values, since the species has not been found experimentally. However, an even shallower PES minimum is predicted for the Ar-species than for its Kr analogue, reflecting the weakness of H-Ar bond. The frequency assigned to the H-Kr stretching of HKrC5N, following the analysis of IR absorption spectra,9 is very far from the presently calculated value, the difference reaching 136 cm-1. This discrepancy rather puts in question the experimental result, than calls for a better theoretical treatment. Indeed, for all other tested cases (Table 2), including the n≠5 HKrCnN species, theory proved to match the experiment quite well. Furthermore, for the three observed HXeCnN compounds, the measured H-Xe frequencies differ by no more than 2 cm-1, and the difference between H-Kr frequencies in HKrCN and HKrC3N is only 5 cm-1. However, the re-examination of spectra resultant from our former experiments did not reveal any plausible candidates for the HKr stretching within the 1450 -1490 cm-1 region.



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3.3. Stability of HRgC5N 3.3.1 HCnN + Rg dissociation channel The B2 dissociation channel (see Introduction) involves the bending mode H-Rg-R. The original HRgCnN molecule and its decay products are separated by a bent transition state (TS). To test the applied theoretical method, we have first carried out the calculations for HXeC2H. The barrier height and the net energetic effect predicted with B3LYP/aug-cc-pVTZ/aug-ccpVTZ-PP differed by -0.1 eV and -0.16 eV from the respective values obtained by Tsivion et al.17 at the CASPT2 level. Both approaches yielded qualitatively similar TS structures. Our calculations performed for the Rg+HCnN dissociation of HRgCnN species (Rg = Ar, Kr, Xe; n= 1, 3, 5) gave energy barriers in the 0.77 – 1.61 eV range, suggesting the possible initialization of such processes with visible or even near-infrared quanta (see Table 3). Barrier heights were predicted to grow with the mass of Rg. Similarly to other noble gases hydrides, HRgCnN molecules are thermodynamically unstable, as indicated by exothermicity of all investigated HRgCnN → HCnN + Rg reactions (the released energy was found to increase with n). The energetics (Table 3) and TS structures (Fig. 5) predicted here for HRgC5N and HRgC3N are mutually similar and quite different from those found for HRgCN. The HRgC3N and HRgC5N compounds were found to dissociate directly via the transition states presented in Fig. 5, contrary to HXeC2H or HRgCN. Even though the TS barrier height predicted for HXeCN is by 0.6 eV lower than that for the isoelectronic HXeC2H molecule, both relevant TS structures are much alike. More precisely, the TS geometry corresponding to the B2 process of HXeCN is far from the one reported by Lundell et al.60 for an analogue dissociation


Page 18 of 45

Page 19 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


channel of HXeC2H, derived with MP2 calculations, but similar to that obtained for the latter molecule using CASPT2

17

; indeed, a reliable theoretical description of such gas-phase

mechanisms necessitates the use of expensive multireference methods, like CASPT2 with a large active space. As mentioned above, HXeC2H and HRgCN do not dissociate directly into Rg and HCN. The first step consists in the production of Xe and HNC, via a TS presented in Fig. 5. Next, HNC may isomerise into HCN.61,62

Figure 5. Transition state structures for HRgCnN → HCnN + Rg reactions (Rg = Ar, Kr or Xe; n=1, 3 or 5), as obtained with B3LYP/aug-cc-pVTZ/aug-cc-pVTZ-PP calculations. Interatomic C-Rg distances given in Å.

Table 3. Energetic effects for HRgCnN → HCnN + Rg reactions, together with corresponding transition state energies (relative, calculated with respect to HRgCnN species), as obtained with B3LYP/aug-cc-pVTZ/aug-cc-pVTZ-PP calculations.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

TS energy (eV)

Page 20 of 45

Reaction energy (eV)

n=1

n=3

n=5

n=1

n=3

n=5

HArCnN

0.77

1.01

0.93

-5.8

-6.0

-6.0

HKrCnN

1.14

1.42

1.35

-5.0

-5.2

-5.2

HXeCnN

1.43

1.64

1.61

-4.2

-4.4

-4.4

3.3.2 H + RgCnN (or H+Rg+CnN) dissociation channel For the majority of discussed matrix-isolated rare gas compounds, the B3 channel (see Introduction), involving the H-Rg stretching mode, was expected to be the main decomposition path for HRgR species.16 As calculated by Tsivion at al. for HXeC2H, the energetic barrier is only slightly higher than the reaction energy (0.98 eV vs. 0.958 eV, respectively).17 Here we estimate the dissociation energies at the B3LYP/aug-cc-pVTZ/augcc-pVTZ-PP level. The dissociation of HRgCnN (Rg=Kr, Xe) species is endothermic, just as for HXeC2H.17 Predicted energetic effects (Table 4) are for HXeCN and HXeC3N slightly higher than those found for HXeC2H17 by Tsivion at al.; in our benchmark calculations endothermicities of HXeC5N and HXeC2H dissociations were practically the same. In general, HRgCN and HRgC3N are predicted to have, for a given Rg atom, very similar B3 dissociation energies. On the other hand, HRgC5N compounds are significant less stable than respective HRgCN or HRgC3N species. The dissociation of Ar-bearing analogues is predicted to be exothermic (by a few tenths of eV), which speaks against its possible creation in matrixes, via the assembly of H, Ar, and CnN. Table. 4. Energetic effects of the HRgCnN → H + Rg + CnN reactions, as predicted with B3LYP/aug-cc-pVTZ/aug-cc-pVTZ-PP calculations.


Page 21 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Reaction energy (eV) n=1

n=3

n=5

HArCnN

-0.3

-0.3

-0.6

HKrCnN

0.5

0.6

0.3

HXeCnN

1.3

1.3

1.1

We conclude that B3 is indeed the most important decay channel for HRgCnN molecules. The B2 can however also be of significance, especially for HXeCN and HXeC3N. Cryogenic environments likely alter the energetics and dynamics of dissociation processes, which, on theoretical grounds, are usually investigated only for the gas-phase. The matrixinduced vibrational frequency shifts can also be huge. As found experimentally,63 the H-Xe stretching frequency of HXeC2H in solid argon or krypton was importantly displaced toward higher energies (see Section 3.1), with respect to the Xe matrix. Similarly, H-Xe vibration frequencies of HXeX compounds (X = H, Cl, Br, CN) are lower in solid xenon 5,59,64 than in other rare gas matrixes. While these findings suggest that the H-Xe bond is more stable in a medium which interacts relatively weakly with embedded molecules (compared to solid Kr or Xe), it should also be recalled that the complexation of HXeX with molecules like e.g. acetylene or carbon dioxide was found65 to result in the increase of H-Xe vibration frequencies, and in the decrease of H-Xe bond distances. Recent studies of Cohen et al.66 suggest that solid xenon environment does not significantly affect the energy barrier involved in the B2 decomposition channel.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

3.4 HRgC5N isomers The B3LYP-based geometry optimisation has been carried out for six species sharing the HRgC5N (hereafter: 1-Rg) stoichiometry, with Rg representing either Kr or Xe. Energy values relative to 1-Rg are given in Fig. 6, together with the bond angles for non-linear molecules. More results – atomic distances and electric dipole moments – regarding the three most stable isomeric modifications of 1-Kr and 1-Xe can be found in Table 5, whereas Table 6 presents the respective vibrational frequencies, IR absorptions intensities, and Raman activities for the fundamental modes.

Figure 6. HRgC5N isomers (Rg=Kr, Xe), as found at the B3LYP/aug-cc-pVTZ/aug-cc-pVTZ-PP level of theory. Indicated energies (relative, calculated with respect to relevant 1-Rg species) are ZPE-corrected; absolute energy values are -709.244386 Hartree and -575.090791 Hartree, for 1Kr and 1-Xe, respectively. Molecules are numbered in the order of increasing energy. See Table 5 for interatomic distances and equilibrium electric dipole moment values; numbering of atoms corresponds to that used in the Table.


Page 22 of 45

Page 23 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 5. Equilibrium bond lengths (Å), Mulliken charges (a.u.), and electric dipole moments (Debye) for the three most stable isomeric modifications of HRgC5N (Rg = Ar, Kr, Xe), as calculated at the B3LYP/aug-cc-pVTZ/aug-cc-pVTZ-PP level of theory. See Fig. 6 for the numbering of atoms.

2-Kr

2-Xe

3-Kr

3-Xe

4-Kr

4-Xe

r(1-2)

1.557

1.739

1.523

1.684

1.556

1.713

r(2-3)

2.310

2.401

2.378

2.451

2.569*

2.676*

r(3-4)

1.223

1.223

1.185

1.186

1.161

1.161

r(4-5)

1.356

1.355

1.315

1.314

1.363

1.366

r(5-6)

1.211

1.211

1.245

1.245

1.255

1.257

r(6-7)

1.300

1.300

1.309

1.309

1.308

1.307

r(7-8)

1.179

1.179

1.265

1.265

1.267

1.267

q(1)

0.045

-0.073

0.158

0.050

0.096

0.096

q(2)

0.560

0.703

0.572

0.727

-0.506

-0.515

q(3)

-0.256

-0.307

-0.563

-0.618

0.172

0.181

q(4)

-0.266

-0.248

0.320

0.346

-0.331

-0.377

q(5)

-0.007

-0.008

-0.281

-0.297

0.193

0.196

q(6)

0.152

0.158

0.214

0.223

-0.290

-0.296

q(7)

-0.528

-0.529

-0.492

-0.500

0.518

0.664

q(8)

0.300

0.305

0.071

0.069

0.148

0.050

µ

10.743

9.880

15.175

15.877

8.368

8.599

* – This entry refers to the distance between atoms 2 and 5 (see Fig. 6).

Both harmonic and anharmonic B3LYP predictions of vibrational frequencies have been obtained for the most stable isomers. In one case (3-Kr) anharmonic frequency calculations gave meaningless (imaginary) numbers, possibly due to a very shallow PES minimum. The weakest among experimentally observed HRgC3N

8

and 1-Rg


9

bands have theoretically


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 45

predicted intensities of about 100 km/mol; relative strengths of the detected vibrations qualitatively matched the B3LYP-derived values. Our current study indicates, for each of the isomers listed in Table 5, at least one vibrational mode giving rise to an IR absorption band of intensity similar or higher compared to the strongest one observed for 1-Rg (corresponding modes generally involve C-N and H-Rg stretchings). Putting aside the discussion of possible formation mechanisms, these computational results offer some prospects for the future detection of 1-Rg isomers. At least in the case of 3-Rg, the expected lower probability of formation, compared to 1-Rg, can possibly be compensated with much stronger IR bands. Based on B3LYP results, overlaps between the isomeric bands are possible. For instance, HRgC4NC (2-Rg) has its C-N and H-Rg stretching bands close to those of 1-Rg, the two species can therefore be mistaken. In fact, the measured band of 1-Rg is relatively broad (typical half-widths of 5 to 10 cm–1), and the satellite bands (possibly originating in disparate matrix sites) are separated by almost 10 cm–1;9 a similar observation was made for HRgC3N.8 Frequency differences between the H-Rg stretching modes of 1-Rg and 2-Rg, calculated with the proposed CCSD(T)-based Morse potential method (see Section 3.2) are larger (ca. 30 cm-1

; see Table 2), and thus the spectral overlaps seem to be less probable.

Table 6. Calculated B3LYP/aug-cc-pVTZ/aug-cc-pVTZ-PP vibrational harmonic (scaled with the factor of 0.96) and anharmonic frequencies, IR absorption intensities (km/mol), and Raman activities (Å4/amu). Mode (symmetry)

νharm, cm

–1

νanharm, –1

cm

IR int.

Rel. IR int.

e

Raman

νharm,

activity

–1

cm

1-Kr

νanharm, –1

cm

IR

Rel.

int.

IR int

Raman e

activity

1-Xe

1 (σ)∗

2238

2286

434

22

4879

2239

2309

419

29

5063

2 (σ)

2173

2225

64

3

1437

2173

2253

58

4

1623

3 (σ)

2040

2095

0

0

664

2041

2126

0

0

745

4 (σ)∗

1774

1513

2011

100

2853

1718

1573

1431

100

2438


Page 25 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


5 (σ)

1167

6 (π)

643

7 (σ)∗

640

8 (π)

1212

73

4

20

1167

8

0

272

610

82

6

14

0

0

4

115

6

9

641

125

9

99

542

4

0

32

537

6

0

28

9 (π)

485

8

0

0

483

6

0

0

10 (π)

265

0

0

2

268

0

0

4

11 (σ)

182

91

5

19

168

84

6

10

12( π)

119

24

2

2

121

18

2

2

13 (π)

34

4

0

0

37

2

0

0

663

182

2-Kr

1245

665

168

2-Xe

1(σ)

2227

2269

41

2

7148

2227

2305

29

2

7532

2(σ)

2105

2160

86

4

28

2106

2206

78

5

53

3(σ)

2004

2056

113

5

1713

2003

2109

132

9

1842

4(σ)

1734

1518

2084

100

2761

1705

1550

1505

100

2400

5(σ)

1200

1245

93

4

22

1201

1293

103

7

16

6(σ)

662

680

96

5

24

663

677

105

7

15

7(π)

647

10

2

582

611

4

0

416

8(π)

498

0

0

76

497

0

0

62

9(π)

412

2

0

14

413

0

0

18

10(π)

253

0

0

0

255

0

0

0

11(σ)

184

93

4

20

171

86

6

11

12(π)

123

42

4

14

126

30

4

12

13(π)

33

16

2

0

36

6

0

0

182

3-Kr

174

3-Xe

1 A'

2136

3773

50

1518

2145

2186

4766

100

378

2 A'

2088

4

0

2186

2096

2144

10

0

1402

3 A'

1867

355

5

209

1868

1913

525

11

131

4 A'

1696

7535

100

30368

1742

1691

3923

82

28424

5 A'

1219

3

0

398

1223

1270

25

1

232



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 45

6 A'

647

2

0

44

652

676

13

0

34

7 A'

553

22

0

211

548

532

25

1

437

8 A"

525

12

0

1

526

268

1

0

138

9 A'

521

13

0

94

522

399

14

0

1

10 A"

505

1

0

0

522

492

16

0

197

11 A'

496

11

0

226

512

450

1

0

29

12 A"

485

12

0

280

504

509

0

0

0

13 A'

257

5

0

652

250

245

26

1

537

14 A"

219

2

0

0

214

214

2

0

0

15 A'

207

24

0

155

204

207

39

1

82

16 A"

97

10

0

22

93

87

14

0

5

17 A'

90

11

0

9

88

75

10

0

6

18 A'

30

9

0

48

38

8

7

0

19

4-Kr

4-Xe

1 A'

2189

2241

249

8

1110

2191

2254

244

13

1034

2 A'

2086

2125

1531

49

383

2081

2125

1689

87

353

3 A'

1855

1905

66

2

147

1850

1904

50

3

144

4 A'

1558

1058

3094

100

4968

1611

1696

1930

100

5160

5 A'

1168

1216

8

0

73

1164

1217

14

1

62

6 A'

654

667

17

1

32

662

673

41

2

22

7 A'

525

537

4

0

42

528

535

10

1

32

8 A"

507

514

2

0

23

508

519

5

0

11

9 A'

486

492

5

0

11

485

501

16

1

15

10 A"

486

494

0

0

23

485

496

0

0

14

11 A'

466

445

62

2

120

450

362

40

2

70

12 A"

445

430

23

1

113

438

362

10

1

76

13 A'

234

235

47

2

59

229

232

66

3

38

14 A"

219

226

2

0

3

220

221

2

0

2

15 A'

180

184

0

0

32

177

177

0

0

23


Page 27 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


16 A"

98

99

6

0

3

99

100

7

0

2

17 A'

78

74

10

0

15

76

88

9

0

14

18 A'

44

39

2

0

42

42

45

2

0

37

* – See Ref. 9 for experimentally observed frequencies of the modes ν 1, ν4 and (tentatively) ν7.

Calculations of the Raman scattering activity indicate at least one strong Raman band for each of the considered lowest-energy isomers. Interestingly, the expected intensities of these bands are higher than for the parent cyanodiacetylene molecule.67 This observation – together with the fact that even the weakest Raman transitions (i.e. by 4 orders of magnitude weaker than the strongest ones) could be measured for matrix-isolated HC5N – speaks for the possible detection of 1-Rg isomers via Raman spectroscopy. An especially intense Raman bands are expected for the isomers 3-Kr and 3-Xe (ν4; see Table 6). Obviously, the photochemical stability of such fragile species has to be taken into account when choosing the excitation wavelengths for Raman measurements. We can only speculate on the formation mechanism for the above discussed isomeric species. Supposedly, 3-Rg and 4-Rg can arise from C5N, once the radical is present in irradiated, HC5N-doped Rg solids. That would be similar to the formation of HRgC5N (or HRgC3N, following the photolysis of HC3N in Kr and Xe matrixes), i.e. to reverse B3 processes, which are expected to be exothermic. Isomer 2-Rg may possibly form from the isonitrile HC4NC, the latter being easily photochemically generated in the course of the UV photolysis.68



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

4. Conclusions Present theoretical study on HRgCnN molecules indicates that any trustworthy description of H-Rg stretching (the vibrational mode crucial in spectroscopic identifications) has to involve an advanced treatment of electron correlation. Indeed, the magnitude of predicted anharmonic effects is strongly influenced by the quality of methods applied for solving the electronic Schrödinger equation, and the calculated harmonic H-Rg frequencies were found to decrease with the increasing computational level – in the order: CCD, CCSD, CCSD(T) – pointing to the importance of electron correlation. The CCSD(T) method was found here to supply the theoretical predictions of very good or at least acceptable quality (considering the size of investigated electronic systems), in particular when combined with the proposed simplified, low-cost anharmonic approach which made use of the Morse-type potential energy function. Calculations indicate that the stabilities of HRgCN, HRgC3N and HRgC5N should be, for a given Rg atom, similar, with a slight preference for HRgC3N. This applies to both HRgCnN → HCnN + Rg and HRgCnN → H + RgCnN decomposition channels. Comparison with the experimental data available for HRgC3N and HRgC5N 8,9, permits us to evaluate the single reference DFT approach as suitable (unlike MP2) for the estimation of energy thresholds governing the H-Rg dissociation. DFT indicates also a low relative stability of HArC5N (the compound was never observed experimentally), compared to analogous Kr- and Xederivatives.


Page 28 of 45

Page 29 of 45

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The computational search for stable molecules sharing the [5C, H, N, Rg] (Rg=Kr, Xe) stoichiometry resulted in verifying the lowest energy of the HRgC5N arrangement, and in selecting 3 next highest stability isomers. Some of these molecules may be detected in future spectroscopic experiments, considering the predicted strong IR absorption and high Raman scattering activity values.

Acknowledgments Authors acknowledge the financial support from the Polish Ministry of Science & Higher Education (grant Iuventus Plus 0441/H03/2010/70). The research was partly supported by the PL-Grid Infrastructure, and National Science Centre (Project No. 2011/03/B/ST4/02763) grants.

References (1)

Maier, G.; Lautz, C. Laser Irradiation of Monomeric Acetylene and the T-Shaped Acetylene Dimer in Xenon and Argon Matrices. Eur. J. Org. Chem. 1998, 1998, 769– 776.

(2)

Feldman, V. I.; Sukhov, F. F.; Orlov, A. Y.; Tyulpina, I. V. Experimental Evidence for the Formation of HXeCCH: The First Hydrocarbon with an Inserted Rare-Gas Atom. J. Am. Chem. Soc. 2003, 125, 4698–4699.

(3)

Tanskanen, H.; Khriachtchev, L.; Lundell, J.; Kiljunen, H.; Räsänen, M. Chemical Compounds Formed from Diacetylene and Rare-Gas Atoms: HKrC4H and HXeC4H. J. Am. Chem. Soc. 2003, 125, 16361–16366.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(4)

Wang, H.; Szczepanski, J.; Vala, M. Infrared Absorption Spectroscopy of the CnXe (n = 2, 3, 5, 7, 9) Species. Phys. Chem. Chem. Phys. 2004, 6, 4090–4095.

(5)

Pettersson, M.; Lundell, J.; Khriachtchev, L.; Räsänen, M. Neutral Rare-Gas Containing Charge-Transfer Molecules in Solid Matrices. III. HXeCN, HXeNC, and HKrCN in Kr and Xe. J. Chem. Phys. 1998, 109, 618–625.

(6)

Khriachtchev, L.; Tanskanen, H.; Lundell, J.; Pettersson, M.; Kiljunen, H.; Räsänen, M. Fluorine-Free Organoxenon Chemistry: HXeCCH, HXeCC, and HXeCCXeH. J. Am. Chem. Soc. 2003, 125, 4696–4697.

(7)

Khriachtchev, L.; Tanskanen, H.; Cohen, A.; Gerber, R. B.; Lundell, J.; Pettersson, M.; Kiljunen, H.; Räsänen, M. A Gate to Organokrypton Chemistry: HKrCCH. J. Am. Chem. Soc. 2003, 125, 6876–6877.

(8)

Khriachtchev, L.; Lignell, A.; Tanskanen, H.; Lundell, J.; Kiljunen, H.; Räsänen, M. Insertion of Noble Gas Atoms into Cyanoacetylene: An Ab Initio and Matrix Isolation Study. J. Phys. Chem. A 2006, 110, 11876–11885.

(9)

Turowski, M.; Gronowski, M.; Guillemin, J.-C.; Kołos, R. Generation of H–Kr–C5N and H–Xe–C5N Molecules. J. Mol. Struct. 2012, 1025, 140–146.

(10) Jayasekharan, T.; Ghanty, T. K. Theoretical Prediction of HRgCO+ Ion (Rg=He, Ne, Ar, Kr, and Xe). J. Chem. Phys. 2008, 129, 184302. (11) Lundell, J.; Pettersson, M.; Khriachtchev, L.; Räsänen, M.; Chaban, G. M.; Gerber, R. B. Infrared Spectrum of HXeI Revisited: Anharmonic Vibrational Calculations and Matrix Isolation Experiments. Chem. Phys. Lett. 2000, 322, 389–394. (12) Khriachtchev, L.; Lundell, J.; Pettersson, M.; Tanskanen, H.; Räsänen, M. Anomalous Isotopic Effect on Vibrational Properties of HXeOH. J. Chem. Phys. 2002, 116, 4758– 4761.


Page 30 of 45

Page 31 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(13) Khriachtchev, L.; Tanskanen, H.; Pettersson, M.; Räsänen, M.; Ahokas, J.; Kunttu, H.; Feldman, V. On Photochemistry of Water in Solid Xe: Thermal and Light-Induced Decomposition of HXeOH and HXeH and Formation of H2O2. J. Chem. Phys. 2002, 116, 5649–5656. (14) Chaban, G. M.; Lundell, J.; Benny Gerber, R. Theoretical Study of Decomposition Pathways for HArF and HKrF. Chem. Phys. Lett. 2002, 364, 628–633. (15) Li, H.; Xie, D.; Guo, H. An Ab Initio Potential Energy Surface and Predissociative Resonances of HArF. J. Chem. Phys. 2004, 120, 4273–4280. (16) Gerber, R. B.; Tsivion, E.; Khriachtchev, L.; Räsänen, M. Intrinsic Lifetimes and Kinetic Stability in Media of Noble-Gas Hydrides. Chem. Phys. Lett. 2012, 545, 1–8. (17) Tsivion, E.; Zilberg, S.; Benny Gerber, R. Predicted Stability of the Organo-Xenon Compound HXeCCH above the Cryogenic Range. Chem. Phys. Lett. 2008, 460, 23–26. (18) Poterya, V.; Votava, O.; Fárník, M.; Ončák, M.; Slavíček, P.; Buck, U.; Friedrich, B. Generation and Orientation of Organoxenon Molecule H–Xe–CCH in the Gas Phase. J. Chem. Phys. 2008, 128, 104313. (19) Tsivion, E.; Gerber, R. B. Stability of Noble-Gas Hydrocarbons in an Organic Liquidlike Environment: HXeCCH in Acetylene. Phys. Chem. Chem. Phys. PCCP 2011, 13, 19601–19606. (20) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J., J. A.; Vreven, T.; Kudin, K. N.; Burant, et al. Gaussian 03, Gaussian, Inc.: Wallingford, CT, USA, 2004. Gaussian 03. (21) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A. Gaussian 09; Gaussian, Inc., Wallingford CT, 2009.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(22) Raghavachari, K.; Trucks, G. W.; Pople, J. A.; Head-Gordon, M. A Fifth-Order Perturbation Comparison of Electron Correlation Theories. Chem. Phys. Lett. 1989, 157, 479–483. (23) Glendening, E. D.; Reed, A. E.; Carpenter, J. E.; Weinhold, F. NBO, Version 3.1; 1988. (24) Becke, A. D. Density‐functional Thermochemistry. III. The Role of Exact Exchange. J. Chem. Phys. 1993, 98, 5648–5652. (25) Møller, C.; Plesset, M. Note on an Approximation Treatment for Many-Electron Systems. Phys. Rev. 1934, 46, 618–622. (26) Head-Gordon, M.; Pople, J. A.; Frisch, M. J. MP2 Energy Evaluation by Direct Methods. Chem. Phys. Lett. 1988, 153, 503–506. (27) Barone, V. Anharmonic Vibrational Properties by a Fully Automated Second-Order Perturbative Approach. J. Chem. Phys. 2005, 122, 014108. (28) Peterson, K. A.; Figgen, D.; Goll, E.; Stoll, H.; Dolg, M. Systematically Convergent Basis Sets with Relativistic Pseudopotentials. II. Small-Core Pseudopotentials and Correlation Consistent Basis Sets for the Post-D Group 16–18 Elements. J. Chem. Phys. 2003, 119, 11113–11123. (29) Kendall, R. A.; Dunning Jr, T. H.; Harrison, R. J. Electron Affinities of the First‐row Atoms Revisited. Systematic Basis Sets and Wave Functions. J. Chem. Phys. 1992, 96, 6796–6806. (30) Peng, C.; Bernhard Schlegel, H. Combining Synchronous Transit and Quasi-Newton Methods to Find Transition States. Isr. J. Chem. 1993, 33, 449–454. (31) Peng, C.; Ayala, P. Y.; Schlegel, H. B.; Frisch, M. J. Using Redundant Internal Coordinates to Optimize Equilibrium Geometries and Transition States. J. Comput. Chem. 1996, 17, 49–56.


Page 32 of 45

Page 33 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(32) Fukui, K. The Path of Chemical Reactions - the IRC Approach. Acc. Chem. Res. 1981, 14, 363–368. (33) Hratchian, H. P.; Schlegel, H. B. Chapter 10 - Finding Minima, Transition States, and Following Reaction Pathways on Ab Initio Potential Energy Surfaces. In Theory and Applications of Computational Chemistry; Scuseria, C. E. D. F. S. K. E., Ed.; Elsevier: Amsterdam, 2005; pp. 195–249. (34) Berski, S.; Latajka, Z.; Silvi, B.; Lundell, J. Electron Localization Function Studies of the Nature of Binding in Neutral Rare-Gas Containing Hydrides: HKrCN, HKrNC, HXeCN, HXeNC, HXeOH, and HXeSH. J. Chem. Phys. 2001, 114, 4349–4358. (35) Pettersson, M.; Khriachtchev, L.; Lundell, J.; Räsänen, M. A Chemical Compound Formed from Water and Xenon: HXeOH. J. Am. Chem. Soc. 1999, 121, 11904–11905. (36) Tanskanen, H.; Khriachtchev, L.; Lundell, J.; Räsänen, M. HXeCCH in Ar and Kr Matrices. J. Chem. Phys. 2006, 125, 074501. (37) Pluta, T.; Avramopoulos, A.; Papadopoulos, M. G.; Leszczynski, J. On the Origin of the Large Electron Correlation Contribution to the Hyperpolarizabilities of Some Diacetylene Rare Gas Compounds. J. Chem. Phys. 2008, 129, 144308. (38) Pettersson, M.; Lundell, J.; Räsänen, M. New Rare-Gas-Containing Neutral Molecules. Eur. J. Inorg. Chem. 1999, 1999, 729–737. (39) Chaban, G. M.; Gerber, R. B. Anharmonic Vibrational Spectroscopy Calculations with Electronic Structure Potentials: Comparison of MP2 and DFT for Organic Molecules. Theor. Chem. Acc. 2008, 120, 273–279. (40) Barone, V.; Biczysko, M.; Bloino, J.; Puzzarini, C. Characterization of the Elusive Conformers of Glycine from State-of-the-Art Structural, Thermodynamic, and Spectroscopic Computations: Theory Complements Experiment. J. Chem. Theory Comput. 2013, 9, 1533–1547.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(41) Barone, V.; Biczysko, M.; Bloino, J.; Puzzarini, C. Accurate Structure, Thermodynamic and Spectroscopic Parameters from CC and CC/DFT Schemes: The Challenge of the Conformational Equilibrium in Glycine. Phys. Chem. Chem. Phys. 2013, 15, 10094–10111. (42) Yagi, K.; Taketsugu, T.; Hirao, K.; Gordon, M. S. Direct Vibrational Self-Consistent Field Method: Applications to H2O and H2CO. J. Chem. Phys. 2000, 113, 1005–1017. (43) Yagi, K.; Hirao, K.; Taketsugu, T.; Schmidt, M. W.; Gordon, M. S. Ab Initio Vibrational State Calculations with a Quartic Force Field: Applications to H2CO,C2H4,CH3OH,CH3CCH, and C6H6. J. Chem. Phys. 2004, 121, 1383–1389. (44) Gronowski, M.; Kołos, R. Ab Initio Studies of the Structure and Spectroscopy of CHNMg Stoichiometry Molecules and van Der Waals Complexes. J. Phys. Chem. A 2013, 117, 4455–4461. (45) Huang, Z. An Ab Initio Potential Energy Surface and Vibrational Energy Levels of HXeO. Chem. Phys. 2009, 359, 34–39. (46) Yanai, T.; Tew, D. P.; Handy, N. C. A New Hybrid Exchange–correlation Functional Using the Coulomb-Attenuating Method (CAM-B3LYP). Chem. Phys. Lett. 2004, 393, 51–57. (47) Iikura, H.; Tsuneda, T.; Yanai, T.; Hirao, K. A Long-Range Correction Scheme for Generalized-Gradient-Approximation Exchange Functionals. J. Chem. Phys. 2001, 115, 3540–3544. (48) Pople, J. A.; Krishnan, R.; Schlegel, H. B.; Binkley, J. S. Electron Correlation Theories and Their Application to the Study of Simple Reaction Potential Surfaces. Int. J. Quantum Chem. 1978, 14, 545–560.


Page 34 of 45

Page 35 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(49) Čížek, J. On the Use of the Cluster Expansion and the Technique of Diagrams in Calculations of Correlation Effects in Atoms and Molecules. In Advances in Chemical Physics; LeFebvre, R.; Moser, C., Eds.; John Wiley & Sons, Inc., 1969; pp. 35–89. (50) Purvis, G. D.; Bartlett, R. J. A Full Coupled‐cluster Singles and Doubles Model: The Inclusion of Disconnected Triples. J. Chem. Phys. 1982, 76, 1910–1918. (51) Scuseria, G. E.; Janssen, C. L.; Schaefer, H. F. An Efficient Reformulation of the Closed‐shell Coupled Cluster Single and Double Excitation (CCSD) Equations. J. Chem. Phys. 1988, 89, 7382–7387. (52) Scuseria, G. E.; Schaefer, H. F. Is Coupled Cluster Singles and Doubles (CCSD) More Computationally Intensive than Quadratic Configuration Interaction (QCISD)? J. Chem. Phys. 1989, 90, 3700–3703. (53) Austin, A.; Petersson, G. A.; Frisch, M. J.; Dobek, F. J.; Scalmani, G.; Throssell, K. A Density Functional with Spherical Atom Dispersion Terms. J. Chem. Theory Comput. 2012, 8, 4989–5007. (54) Dunning, T. H. J. Gaussian Basis Sets for Use in Correlated Molecular Calculations. I. The Atoms Boron through Neon and Hydrogen. J. Chem. Phys. 1989, 90, 1007–1023. (55) Woon, D. E.; Dunning, T. H. J. Gaussian Basis Sets for Use in Correlated Molecular Calculations. III. The Atoms Aluminum through Argon. J. Chem. Phys. 1993, 98, 1358–1371. (56) Peterson, K. A.; Puzzarini, C. Systematically Convergent Basis Sets for Transition Metals. II. Pseudopotential-Based Correlation Consistent Basis Sets for the Group 11 (Cu, Ag, Au) and 12 (Zn, Cd, Hg) Elements. Theor. Chem. Acc. 2005, 114, 283–296. (57) Figgen, D.; Rauhut, G.; Dolg, M.; Stoll, H. Energy-Consistent Pseudopotentials for Group 11 and 12 Atoms: Adjustment to Multi-Configuration Dirac–Hartree–Fock Data. Chem. Phys. 2005, 311, 227–244.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(58) Rappoport, D.; Furche, F. Property-Optimized Gaussian Basis Sets for Molecular Response Calculations. J. Chem. Phys. 2010, 133, 134105. (59) Pettersson, M.; Lundell, J.; Räsänen, M. Neutral Rare‐gas Containing Charge‐transfer Molecules in Solid Matrices. I. HXeCl, HXeBr, HXeI, and HKrCl in Kr and Xe. J. Chem. Phys. 1995, 102, 6423–6431. (60) Lundell, J.; Cohen, A.; Gerber, R. B. Quantum Chemical Calculations on Novel Molecules from Xenon Insertion into Hydrocarbons. J. Phys. Chem. A 2002, 106, 11950–11955. (61) Isaacson, A. D. Including Anharmonicity in the Calculation of Rate Constants. 1. The HCN/HNC Isomerization Reaction†. J. Phys. Chem. A 2005, 110, 379–388. (62) Booth, D.; Murrell, J. N. Quantum Mechanical Calculations of the HCN-HNC Isomerization. Mol. Phys. 1972, 24, 1117–1122. (63) Tanskanen, H.; Khriachtchev, L.; Lundell, J.; Räsänen, M. HXeCCH in Ar and Kr Matrices. J. Chem. Phys. 2006, 125, 074501. (64) Lorenz, M.; Räsänen, M.; Bondybey, V. E. Neutral Xenon Hydrides in Solid Neon and Their Intrinsic Stability†. J. Phys. Chem. A 2000, 104, 3770–3774. (65) Lignell, A.; Khriachtchev, L. Intermolecular Interactions Involving Noble-Gas Hydrides: Where the Blue Shift of Vibrational Frequency Is a Normal Effect. J. Mol. Struct. 2008, 889, 1–11. (66) Cohen, A.; Tsuge, M.; Khriachtchev, L.; Räsänen, M.; Gerber, R. B. Modeling of HXeBr in CO2 and Xe Environments: Structure, Energetics and Vibrational Spectra. Chem. Phys. Lett. 2014, 594, 18–22. (67) Turowski, M.; Crépin, C.; Douin, S.; Gronowski, M.; Couturier-Tamburelli, I.; Piétri, N.; Wasiak, A.; Kołos, R. Low Temperature Raman Spectra of Cyanobutadiyne (HC5N). Vib. Spectrosc. 2012, 62, 268–272.


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(68) Coupeaud, A.; Turowski, M.; Gronowski, M.; Piétri, N.; Couturier-Tamburelli, I.; Kołos, R.; Aycard, J.-P. Spectroscopy of Cyanodiacetylene in Solid Argon and the Photochemical Generation of Isocyanodiacetylene. J. Chem. Phys. 2007, 126, 164301.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 ACS Paragon Plus Environment

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23


Ar: +0.18 Kr: +0.06 Xe: -0.06

Ar: 1.4468 Kr: 1.5511 Xe: 1.7213

+0.46 +0.56 +0.70

-0.30 -0.28 -0.26

-0.21 -0.23 -0.28

2.2676 2.3075 2.4022

1.2351 1.2351 1.2351

+0.07 +0.07 +0.07

1.3688 1.3690 1.3689


-0.12 -0.12 -0.11

1.2233 1.2231 1.2227

+0.21 +0.21 +0.20

1.3752 1.3751 1.3747

-0.28 -0.27 -0.27

1.1695 1.1694 1.1693


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

a)

Page 40 of 45

175 Xe

H-Rg bond length, pm

170 165 160

Kr 155 150 Ar

145

1

2

3

4

5

Number of carbon atoms 245

b)

Xe

Rg-C bond length, pm

240

235 Kr 230 Ar 225 1

2

3

4

ACS Paragonof Plus Environment Number carbon atoms

5

Page 41 of 45

Energy, Hartree Energy, Hartree

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


-631.55245 -631.55250 -631.55255 -631.55260 -631.55265 -631.55270 -631.55275 -631.55280 -631.55285 -631.55290

1.50

1.52

1.54

1.56

1.58

H-Kr Angstroms H-Krdistance, distance, Å ACS Paragon Plus Environment

1.60


Energy, Hartree Energy, Hartree

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

Page 42 of 45

-497.66380 -497.66385 -497.66390 -497.66395 -497.66400 -497.66405 -497.66410 -497.66415 -497.66420 -497.66425 -497.66430 -497.66435

1.68

1.70

1.72

1.74

H-Xe Angstroms H-Xedistance, distance, Å ACS Paragon Plus Environment

1.76

1.78

Page 43 of 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


2.76

Ar

2.59

Kr

2.70

Xe

2.83

2.75

2.86

2.89

2.90

2.92



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

3 Kr: 26 kcal/mol Xe: 28 kcal/mol

Page 44 of 45


1 0 kcal/mol

2 Kr: 27 kcal/mol Xe: 27 kcal/mol 5 Kr: 52 kcal/mol Xe: 46 kcal/mol 6 Kr: 58 kcal/mol Xe: 58 kcal/mol



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Morse potential 3.0

Relative Energy, eV

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


vibrational frequency

Calc.= 1596 cm-1 Exp. = 1622 cm-1

2.5 2.0

Isomers

1.5 1.0 0.5 0.0 1.0

1.5

2.0

2.5

3.0

3.5

distance, Å


4.0

Quantum Chemical Study on HKrC5N, HXeC5N, and Related Rare

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