Multidimensional Large Amplitude Dynamics in the ... - ACS Publications

Subscriber access provided by Fudan University

Article

Multidimensional Large Amplitude Dynamics in the Pyridine – Water Complex Rebecca B Mackenzie, Christopher T Dewberry, Ryan D. Cornelius, Christopher J. Smith, and Kenneth R. Leopold J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.6b11255 • Publication Date (Web): 05 Jan 2017 Downloaded from http://pubs.acs.org on January 16, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry A is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 25

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

The Journal of Physical Chemistry

December 27, 2016 J. Phys. Chem. A Revised

Multidimensional Large Amplitude Dynamics in the Pyridine – Water Complex

Rebecca B. Mackenzie,(a) Christopher T. Dewberry,(b) Ryan D. Cornelius,(c) C.J. Smith,(a) and Kenneth R. Leopold(a),*

(a) Department of Chemistry, University of Minnesota, 207 Pleasant St., SE, Minneapolis, MN 55455 (b) Department of Chemistry and Biochemistry, Kettering University, 1700 University Ave. Flint, MI 48504 (c) Department of Chemistry and Biochemistry, St. Cloud State University, 720 4th Avenue South, St. Cloud, MN 56301 *Corresponding Author: E-mail: [email protected]

1 ACS Paragon Plus Environment


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

Abstract Aqueous pyridine plays an important role in a variety of catalytic processes aimed at harnessing solar energy. In this work, the pyridine-water interaction is studied by microwave spectroscopy and DFT calculations. Water forms a hydrogen bond to the nitrogen with the oxygen tilted slightly toward either of the ortho hydrogens of the pyridine, and a tunneling motion involving in-plane rocking of the water interconverts the resulting equivalent structures. A pair of tunneling states with severely perturbed rotational spectra is identified and their energy separation, ∆E, is inferred from the perturbations and confirmed by direct measurement. Curiously, values of ∆E are 10404.45 MHz and 13566.94 MHz for the H2O and D2O complexes, respectively, revealing an inverted isotope effect upon deuteration. Small splittings in some transitions suggest an additional internal motion making this complex an interesting challenge for theoretical treatments of large amplitude motion. The results underscore the significant effect of the orthohydrogens on the intermolecular interaction of pyridine.


Page 2 of 25

Page 3 of 25

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


Introduction The interaction of pyridine (py) and water underlies a variety of topics in sustainable energy research. The py−H2O complex, for example, has been investigated for its possible role in photoinduced bond cleavage of water1 and both pyridine and pyridinium are prominent in studies on photoelectrochemical mechanisms for CO2 reduction.2 Solvent-solute interactions play an important role in the photophysics of pyridine solutions3 and calculations indicate that n-π* excitation induces significant structural rearrangement of the py−H2O complex.4 Detailed information about the pyridine-water interaction should be a valuable part of our understanding of a variety of environmentally friendly photochemical processes.

Nearly 20 years ago, Caminati et al. reported microwave spectra of the three diazine–water complexes.5-7 In each case, the primary interaction is an N⋅⋅⋅HO hydrogen bond that is rendered nonlinear, presumably by a secondary attraction between the oxygen and an available orthohydrogen. Moreover, in the case of pyrazine, which has D2h symmetry and two available ortho hydrogens, the complex with water has two degenerate minimum energy configurations. These produce a pair of tunneling states whose energy separation was determined by direct observation of spectroscopic transitions that cross between them.5 More recently, the complex of water with pentafluoropyridine has been studied and shown to adopt a very different geometry, in which the water oxygen lies above the plane of the ring.8 Curiously, however, analogous studies of the py−H2O complex have not been reported. Low resolution gas phase infrared spectra have been published,9 and some microwave spectra have been collected,10 but the latter appear to have been too complex to assign at the time. With the aid of modern, broadband chirped-pulse spectroscopy,11 we have investigated both the H2O and D2O isotopologues of the system. The spectra reveal an interaction rich with internal dynamics that perturb the spectra so strongly that they would have been difficult, if not impossible, to unravel using older methods alone. They provide an interesting test case for theoretical treatments of large amplitude motion on complex potential energy surfaces and, moreover, further demonstrate the significant role of the ortho hydrogens in the intermolecular interactions of pyridine.



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 4 of 25

Methods and Results Prior to experimentation, density functional theory (DFT) was used to predict the minimum energy

structure

of

py–H2O.

The

main

theoretical

results

obtained

from

M06-2X/6-311++G(3df,3pd) calculations, are presented in Table 1. Atom numbering and the orientation of the inertial axis system are shown in Fig. 1. Additional details are provided as Supporting Information. As with the diazine-H2O complexes, and in accord with previous computational work,12 the system exhibits a nonlinear hydrogen bond. The transition state connecting the two degenerate bent configurations is a symmetric, linearly hydrogen bonded structure and the associated imaginary frequency corresponds to an in-plane rocking motion with a barrier of 0.33 kcal/mol (Fig. 2a). This motion is similar to that described for pyrazine−H2O5 and to that recently observed for py−HCCH.13 The binding energy at this level of theory is 7.0 kcal/mol.

The spectroscopic consequence of the finite barrier in Fig. 2a is a lifting of the degeneracy associated with the two equivalent configurations, producing a closely-spaced pair of tunneling states. Moreover, the motion shown inverts µb, but not µa or µc, where µg is the dipole moment component along the g-inertial axis (see Fig. 1). Thus, we anticipate that a- and c-type rotational transitions occur within a tunneling state, producing a doubling of their spectra (one set for each state). The b-type transitions, on the other hand, should cross from the ground to the excited tunneling state and provide a direct measure of the tunneling splitting.

Spectra were obtained by entraining the vapor above a 5:1 mixture of pyridine : water in Ar and expanding at a stagnation pressure of 2 atm, into our tandem chirped-pulse, cavity Fourier transform microwave spectrometer.14,15 A 3D-printed slit nozzle15 (0.0085″ x 1.25″) was used to increase the signal-to-noise ratio. Chirped-pulse spectra between 6 and 18 GHz were taken in 3 GHz segments and line frequencies were measured to ~40 kHz. High resolution cavity measurements had a spectral resolution of ~4 kHz. Additional details regarding the spectrometer and molecular source are given elsewhere.14,15

Initially, a chirped-pulse spectrum from 6-18 GHz permitted the assignment of a series of Rbranch a-type K−1 = 0 transitions, which were eventually attributed to the ground state. However, 4 ACS Paragon Plus Environment

Page 5 of 25

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


despite substantial efforts, no additional transitions could be identified based on a semi-rigid rotor model. Similar results were obtained for py−D2O. Eventually,

14

N nuclear hyperfine

structure obtained by re-measuring observed transitions at high resolution on the cavity spectrometer provided the key for identifying transitions involving K−1 = 1 for both isotopologues. These transitions were far removed from predictions based on a semi-rigid rotor Hamiltonian, sometimes by hundreds of MHz, indicating that the spectra were highly perturbed. Such perturbations between tunneling states are common, though their severity in this case was extraordinary.

Further analysis of the chirped-pulse spectrum, as well as measurements of the

14

N nuclear

hyperfine structure obtained on the cavity spectrometer, led to the identification of transitions belonging to the excited tunneling state. The severity of the perturbation is illustrated in Fig. 3, where it is seen that the relative positions of the ground and excited state transitions is a strong function of the rotational quantum number, J. Nonetheless, using Pickett’s SPFIT program,16 the spectra were readily fit to a Hamiltonian of the form = + + + +

(1)

= +

(2)

where

HRot and HCD are the rigid rotor and Watson A-reduced centrifugal distortion Hamiltonians, respectively and HInt is the interaction term between the two states with the Coriolis coupling constant Fab. HTun is the energy separation between the states, ∆E, and is added only for the upper state. Hhfs describes the

14

N nuclear hyperfine structure. The resulting constants provided

accurate predictions for transitions involving K−1 = 2 of both tunneling states as well as three btype transitions that cross between the tunneling states. c-type transitions were not observed despite the large calculated value of µc (1.2 D). A number of py-H2O transitions, particularly those involving K−1 > 0 in the excited state, showed a small doubling, typically between 20 and 500 kHz, as illustrated in Fig. 4. For those lines, the most intense set of components was selected for analysis. In the final fit of all assigned lines, a small distortion term, −FabJ × J(J+1), was added to Fab. Considering that the secondary splitting was not addressed in the analysis, the rms 5 ACS Paragon Plus Environment


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

residual of 15 kHz obtained for the py−H2O spectral fit was considered excellent. For the D2O fit, which was further complicated by unresolved deuterium hyperfine structure, the 20 kHz rms residual was also deemed entirely acceptable. Unsurprisingly, however, a few residuals were as large as 52 and 84 kHz for H2O and D2O fits, respectively. Spectroscopic constants are given in Table 2, and the fitted rotational constants are seen to be in good agreement with DFT results of Table 1. The calculated inertial defects are positive and unexpectedly large, likely indicating that the fitted rotational constants, while corrected for the primary perturbation, remain somewhat contaminated by Coriolis contributions arising from the additional, untreated motion(s).

Discussion The observed b-type transitions provide direct, unambiguous measures of ∆E. Remarkably, however, ∆E is seen to increase upon deuteration, counter to expectation were it purely the tunneling energy associated with the motion of Fig. 2a. A clue to the origin of this anomaly may lie in the additional doubling of some of the spectra noted above, as these “extra” splittings reveal the existence of tunneling states associated with another pair of equivalent configurations. Furthermore, the absence of c-type transitions at their rigid rotor locations suggests a motion that inverts µc, causing either the average of µc (and hence the corresponding intensities) to vanish or requiring the c-type transitions to cross an associated tunneling doublet, thus displacing them from their predicted positions by an unknown amount. Two possible motions are a cross-plane wag of the free water hydrogen or a rotation of the water about an axis perpendicular to its plane that interchanges the bound and free hydrogens (Figs. 2b,c). Further DFT calculations revealed 0.07 and 2.23 kcal/mol barriers for these motions, respectively. However, if the 0.07 kcal/mol barrier is a computational artifact, as its small value may suggest, the equilibrium geometry would be planar. In this case, the vibrationally averaged µc would be zero, presenting a third scenario in which the second pair of tunneling states arises from an exchange of the hydrogens by a rotation of the water about its C2 axis (Fig. 2d). In any case, the existence of a second motion is supported by the second set of splittings, a few abnormally large residuals, and the rather high inertial defect. Further studies on the HDO isotopologues will be necessary to further elucidate the nature of the second motion.


Page 6 of 25

Page 7 of 25

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


Fig. 5 illustrates how a second large amplitude motion could produce the anomalous isotopic dependence of ∆E. Two splittings are shown: ∆E1 arises from motion along the coordinate of Fig. 2a; ∆E2 and ∆E2′ arise from a water-centered internal motion and may differ for the upper and lower states of the rocking motion. The ∆E determined in this work is a composite quantity, viz. ∆E = ∆E1 + (∆E2 − ∆E2′ )/2. While ∆E1, ∆E2, and ∆E2′ should all decrease slightly upon deuteration, ∆E2 and ∆E2′ will be more sensitive and may change by different amounts. If the change in (∆E2 − ∆E2′ )/2 upon deuteration offsets that in ∆E1, an anomalous isotope dependence can be realized. While quantitative details of the diagram remain to be clarified, it serves to illustrate the complexity than can pervade systems with multiple large amplitude motions.

Another factor contributing to the increase in tunneling splitting upon deuteration may involve differences in tunneling path resulting from the degree to which the H2O and D2O species sample the potential energy surface. Caminati and coworkers have observed a 5% increase in the tunneling splitting associated with a butterfly-like motion in the cyclobutanone – HCOOH complex upon deuteration in the OH position of the formic acid.17 Although no detailed calculations were performed for the HCOOD isotopologue, the effect was attributed to a change in tunneling path resulting from a decrease in the heavy atom distance associated with deuteration in the hydrogen bond, i.e., the Ubbelohde effect, which this group has studied extensively. While an analogous effect may contribute to the 30% rise in ∆E upon deuteration reported here, the observation of several internal motions in py−H2O suggests that a multidimensional treatment that includes the possibility of superimposed tunneling energies (as suggested in Fig. 5), is likely to be required.

The complex internal dynamics in this system arise, at least in part, from the existence of a pair of equivalent configurations associated with a tilt of the water unit toward one of the two ortho hydrogens of the pyridine ring. An attraction between the water oxygen and the ortho hydrogens likely gives rise to this tilt. Indeed, the significance of similar secondary interactions has been noted in a number of related systems. As previously discussed, for example, the diazine – water complexes have nonlinear hydrogen bonds, likely resulting from analogous secondary interactions. Moreover, the short van der Waals bond lengths and lack of internal rotation in the complexes py−CO218 and 3,5-difluoropyrine−CO219 have been attributed to the secondary 7 ACS Paragon Plus Environment


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

hydrogen bonds between the CO2 oxygens and ortho hydrogens. In the py−HCCH complex,13 the acetylene forms a hydrogen bond to the nitrogen, but tilts so as to bring its π electron density closer to one or the other of the ortho hydrogens, producing complex internal dynamics similar to those observed here.

That such an interaction gives rise to severe perturbations in py−H2O could not have been easily anticipated. A comparison of pyridine−water and pyrazine–water underscores the challenge: The two systems are chemically and structurally very similar, yet the pair of tunneling states observed for pyrazine – water exhibited straightforward rotational spectra whose analysis did not require even a small Coriolis coupling term.5 The severity of the perturbations in py−H2O likely arises from the combined effects of details of the potential energy surface and the effective mass for the tunneling motion which, together, sensitively determine the tunneling splitting. Combined with the possibility of additional motion on the water subunit, these features produce tunneling energies that allow for accidental near degeneracies between Coriolis coupled rotational states, thus producing the extraordinary perturbations observed. Without the ability to predict rotationvibration-tunneling energies on complex potential surfaces with very high accuracy, the need to treat system-dependent degrees of perturbation will likely continue to be realized on the basis of empirical discovery rather than a priori prediction.

In summary, the py−H2O complex has been studied by microwave spectroscopy and density functional theory. The system has a nonlinear N⋅⋅⋅HO hydrogen bond and a binding energy of 7.0 kcal/mol at the M06-2X/6-311++G(3df,3pd) level. The nonlinearity of the hydrogen bond provides another example of the influence of the ortho hydrogens on the intermolecular interactions of pyridine and gives rise to unusually strong perturbations in the rotational spectrum. These perturbations reveal complex internal dynamics that include a rocking between equivalent configurations in the heavy atom plane. Cross-plane wagging of the free water hydrogen and/or a hydrogen-exchanging internal rotation of the water unit are also implicated. Two pairs of tunneling states are observed and the compound motions likely give rise to an unexpected isotope dependence of the measured tunneling energy. This feature should provide a challenging test case for theoretical treatments of multidimensional large amplitude dynamics. Additional work on the HDO complex is in progress. Future work should focus on accessing 8 ACS Paragon Plus Environment

Page 8 of 25

Page 9 of 25

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


additional tunneling states (Fig. 5) to further define the water-centered motion, and on elucidating the effects of the double well potential and facile tunneling dynamics on the photophysics of aqueous pyridine.

Supplementary Material Available The Supporting Information is available free of charge on the ACS Publications website at xxxx.

Tables of observed frequencies, assignments, and residuals from the least squares fits. Cartesian coordinates for the calculated minimum energy structure. Cartesian coordinates for the transition states associated with different water-centered motions.

Acknowledgments This work was supported by the National Science Foundation, Grant Nos. CHE-1266320 and CHE-1563324, a UMN Doctoral Dissertation Fellowship awarded to R.B.M., the Minnesota Supercomputer Institute, and a Lando Summer Undergraduate Research Fellowship awarded to R.D.C. through the University of Minnesota. We thank Prof. Renee Frontiera for bringing this problem to our attention and to Dr. Jon Hougen for some helpful correspondence.



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

References

1. Liu, X.; Sobolewski, A.L.; Domcke, W. Photoinduced Oxidation of Water in the PyridineWater Complex: Comparison of the Singlet and Triplet Photochemistries. J. Phys. Chem. A 2014, 118, 7788-7795. 2. White, J.L.; Baruch, M.F.; Pander III, J.E.; Hu, Y.; Fortmeyer, I.C.; Park, J.E.; Zhang, T.; Liao, K.; Gu, J.; Yan, Y.; Shaw, T.W.; Abelev, E.; Bocarsly A.B, Light-Driven Heterogeneous Reduction of Carbon Dioxide: Photocatalysts and Photoelectrodes. Chem. Rev. 2015, 115, 12888-12935. 3. Chachisvilis, M.; Zewail, A.H. Femtosecond Dynamics in the Condensed Phase: Valence Isomerization by Conical Intersections. J. Phys. Chem. A 1999, 103, 7408-7418. 4. Remiers, J.R.; Cai, Z.-L. Hydrogen Bonding and Reactivity of Water to Azines in the S1 (n,π*) Electronic Excited States in the Gas Phase and in Solution. Phys.Chem.Chem.Phys. 2012, 14, 8791-8802. 5. Caminati, W.; Favero, L.B.; Favero, P.G.; Maris, A.; Melandri, S. Intermolecular Hydrogen Bonding Between Water and Pyrazine, Angew. Chem. Int. Ed. 1998, 37, 792-795. 6. Melandri, S.; Sanz, M.E.; Caminati, W.; Favero, P.G.; Kisiel, Z. The Hydrogen Bond between Water and Aromatic Bases of Biological Interest: An Experimental and Theoretical Study of the 1:1 Complex of Pyrimidine with Water. J. Am. Chem. Soc. 1998, 120, 11504-11509. 7. Caminati, W.; Moreschini, P.; Favero, P.G. The Hydrogen Bond between Water and Aromatic Bases of Biological Interest: Rotational Spectrum of Pyridazine-Water. J. Phys. Chem. A 1998, 102, 8097-8100. 8. Calabrese, C.; Gou, Q.; Maris, A.; Caminati, W.; Melandri, S. Probing the Lone-Pair⋅⋅⋅π-Hole Interaction in Perfluorinated Heteroaromatic Rings: The Rotational Spectrum of Pentafluoropyridine-Water. J. Phys. Chem. Lett. 2016, 7, 1513-1517. 9. Millen, D.J.; Mines, G.W. Hydrogen Bonding in the Gas Phase. J. Chem. Soc. Farad. Trans. 2 1977, 73, 369-377. 10. Kuczkowski R.L. in Microwave Information Letters XXXVIII., Lovas, F.J., Ed. 1995. p. 37. 11. Brown, G.G.; Dian, B.C.; Douglass, K.O.; Geyer, S.M.; Shipman, S.T.; Pate, B.H. A Broadband Fourier Transform Microwave Spectrometer Based on Chirped Pulse Excitation. Rev. Sci. Instrumen. 2008, 79, 053103-1-13. 10 ACS Paragon Plus Environment

Page 10 of 25

Page 11 of 25

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


12. Sicilia, M.C.; Muñoz-Caro, C.; Niño, A. Theoretical Analysis of Pyridine Protonation in Water Cluster of Increasing Size. ChemPhysChem. 2005, 6, 139-147. 13. Mackenzie, R.B.; Dewberry, C.T.; Coulston, E.; Cole, G.C.; Legon, A.C.; Tew, D.P.; Leopold, K.R. Intramolecular Competition between n-Pair and π-Pair Hydrogen Bonding: Microwave Spectrum and Internal Dynamics of the Pyridine-Acetylene Hydrogen-Bonded Complex. J. Chem. Phys. 2015, 143, 104309-1-10. 14. Phillips, J.A.; Canagaratna, M.; Goodfriend, H.; Grushow, A.; Almlöf, J.; Leopold, K.R. Microwave and ab Initio Investigation of HF−BF3. J. Am. Chem. Soc. 1995, 117, 1254912556. 15. Dewberry, C.T.; Mackenzie, R.B.; Green, S.; Leopold, K.R. 3D-Printed Slit Nozzles for Fourier Transform Microwave Spectroscopy. Rev. Sci. Instum. 2015, 86, 065107-1-7. 16. Pickett, H.M. The Fitting and Prediction of Vibration-Rotation Spectra with Spin Interactions. J. Mol. Spectrosc., 1991, 148, 371-377. 17. Evangelisti, L.; Spada, L.; Li, W.; Blanco, S.; López, J.C.; Lesarri, A.; Grabow, J.-U.; Caminati, W. A Butterfly Motion of Formic Acid and Cyclobutanone in the 1:1 Hydrogen Bonded Molecular Cluster. Phys. Chem. Chem. Phys. 2017, 19, 204-209. 18. Doran, J.L.; Hon, B.; Leopold, K.R. Rotational Spectrum and Structure of the Pyridine−CO2 van der Waals Complex. J. Mol. Struct. 2012, 1019, 191-195. 19. Dewberry, C.T.; Cornelius, R.D.; Mackenzie, R.B.; Smith, C.J.; Dvorak, M.A.; Leopold, K.R. Microwave Spectrum and Structure of the 3,5-Difluoropyridine⋅⋅⋅CO2 van der Waals Complex. J. Mol. Spectrosc. 2016, 328, 67-72.



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 1. Theoretical Results for the Minimum Energy Structure of py− −H2O from M06-2X/6-311++G(3df,3pd) Calculationsa A [MHz] 6001(1.2) B [MHz] 1514(1.2) C [MHz] 1212(3.5)

∆ΙD [u⋅Å2]b µa [D] µb [D] µc [D]

−1.0 3.57

R(H10-O2) [Å] R(N4-H3) [Å]

2.69 1.95 159

0.46 1.20

∠ (C7-N4-H3) [deg]

156 ∠ (N4-H3-O2) [deg] (a) Values in parentheses are the percent difference relative to the experimental ground state values. (b) Inertial defect, defined by Δ = − − .


Page 12 of 25

Page 13 of 25

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 2. Spectroscopic Constants for Py− −H2O and Py− −D2O.a Py− −H2Ob 5932.09(12) 1495.6117(57) 1171.4302(57) 8.3 5912.50(38) 1498.5063(77) 1172.2425(69) 8.4 −4.352(11) −1.787(31) -4.525(17) −1.81(14) 1.275(33) 1.107(29) 0.399(19) 0.357(30) 12.2(11) 45.9(16) 9.6(28) 28.4(36) 10404.45(12) 417.1488(70) −7.91(18) 15 133

A″/MHz B″/MHz C″/MHz ΔID″ /u·Å2 d A′/MHz B′/MHz C′/MHz ∆ID′/ u·Å2 d 14 N χaa″/MHz 14 N (χbb – χcc)″/MHz 14 N χaa′/MHz 14 N (χbb – χcc)′/MHz ∆J″/kHz ∆J′/kHz δJ″/kHz δJ′/kHz ∆JK″/kHz ∆JK′/kHz δK″/kHz δK′/kHz ∆E/MHz Fab/MHz FabJ/kHz RMS/kHz N

Py− −D2Ob,c 5906.45(12) 1403.7800(60) 1115.6702(64) 7.4 5868.68(34) 1407.1414(73) 1116.6034(62) 7.3 −4.401(15) −1.900(88) −4.511(37) −1.81(19) 1.074(32) 0.917(29) 0.335(17) 0.278(27) 10.54(91) 46.7(14) 8.0(30) 23.9(30) 13566.94(12) 383.1749(75) -7.01(17) 20 123

(a) Double and single primes refer to the lower and upper states, respectively. (b) For rotational transitions with additional doubling, the most intense set of components was selected. (c) Deuterium hyperfine structure was too collapsed to analyze.

(d) Δ = − −



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 14 of 25

Figure Captions

Figure 1. The minimum energy structure of py−H2O from M06-2X/6-311++G(3df,3pd) calculations. The orientation of the inertial axis system, (a,b,c), is also shown. Figure 2. (a) Depiction of the in-plane rocking motion in py–H2O from M06-2X/6-311++G(3df,3pd) calculations. (b,c,d) Possible water-centered motions. Calculated barrier heights are reported for each motion. Figure 3. Five segments of the py–H2O chirped-pulse spectrum showing a-type K=0 transitions for the ground (blue) and excited (red) states. Ground state K=0 intensities were normalized to facilitate comparison of relative intensities. The green transition in the J = 4 ← 3 region is the excited state 413 ← 312 line and the green transition in the J = 5 ← 4 region is the excited state 523 ← 422 line. Figure 4. Cavity spectra of the 312←211 transition for the ground (a) and excited (b) states of pyH2O. 14N hyperfine structure is evident. The excited state displays a second set of transitions, marked with ◊ and offset by 270 kHz from the more intense set marked with ●. Similar structure in the ground state appears as barely resolved shoulders.

Figure 5. Qualitative energy diagram illustrating the possible effect of deuterium substitution on the observed value of ∆E. Based on our current understanding of this system, ∆E measured in this work is between the ground and excited rocking states with no change from ground to excited water-related levels.


Page 15 of 25

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

b c

Figure 1



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 16 of 25

Figure 2


Page 17 of 25

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


Figure 3



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 18 of 25

Figure 4


Page 19 of 25

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


Figure 5



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 20 of 25

Page 21 of 25

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

b c

Figure 1



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

Page 22 of 25

Page 23 of 25





Page 24 of 25

Page 25 of 25



Multidimensional Large Amplitude Dynamics in the ... - ACS Publications

Recommend Documents