Hemibonding between Water Cation and Water - The Journal of

Subscriber access provided by University of Otago Library

Article

Hemibonding Between Water Cation and Water Daniel M. Chipman J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.6b09905 • Publication Date (Web): 10 Nov 2016 Downloaded from http://pubs.acs.org on November 14, 2016

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 21

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

Hemibonding Between Water Cation and Water Daniel M. Chipman* Radiation Laboratory, University of Notre Dame, Notre Dame, Indiana 46556-5674∗

Abstract The hemibonding interaction in water dimer cation is studied using coupled cluster electronic structure methods. The hemibonded dimer cation geometry is a local minimum structure characterized by the two participating monomers having both a very short separation and a near parallel relative orientation. It is shown that the vertically ionized dimer at its optimum neutral geometry can convert to the hemibonded dimer cation structure with essentially no energetic hindrance. Direct conversion to the hemibonded structure is therefore an energetically facile alternative to the minimum energy path that connects the vertically ionized neutral water dimer to the global minimum proton-transferred structure. A substantial barrier must be surmounted to convert the hemibonded dimer cation to the proton-transferred structure. The optical absorption spectrum of the hemibonded dimer cation is characterized by three excited near-UV states, two of which have very large oscillator strengths. Relative resonance Raman intensities are estimated for the hemibonded dimer cation vibrational modes, finding the intermolecular stretching mode to be the most strongly enhanced when in near resonance with each of the near-UV excited states, and the anharmonicity and overtones of this mode are estimated. These results provide guidance for the possible observation of hemibonded cations in irradiated liquid water.

ACS Paragon 1 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

INTRODUCTION

The main elementary process occurring in the radiolysis of liquid water is an ionization event producing water cation and an electron.1–3 The vertically born water cation can immediately transfer a proton to an adjacent hydrogen-bonded water molecule, thereby forming hydronium cation and hydroxyl radical, which process has experimentally been determined to occur on a femtosecond time scale.4,5 Experiments and AIMD simulations further indicate that an initially partially delocalized cationic hole localizes within about 30 fs after which proton transfer to a neighboring water molecule proceeds practically immediately.6 With high concentrations of anions the initial radiolytically-produced water cation can alternatively be reduced back to neutral water by ultrafast electron transfer from a contact anion.7–9 These options do not rule out the possibility of some water cations having a sufficient lifetime to be observable as such. Water cations would be very strong oxidizing agents, and their presence could affect the early chemistry taking place during radiolysis of water solutions. To gain further insight studies have also been carried out on ionized water clusters, where the proton transfer upon ionization has been experimentally established10–13 and electronic structure calculations have characterized the global minimum proton-transferred structure.11,14–41 Dynamics of the proton transfer process have additionally been calculated with AIMD in ionized water clusters.31,35,42–51 A number of calculations have also reported the existence of a secondary local minimum corresponding to a hemibonding structure19–21,23–30,32,34–36,38,39,42,43,45,49,50,52,53 and several have characterized the transition state19,25,26,34,50 connecting hemibonded and protontransferred structures. The hemibond in this case can be qualitatively described as a 2 center-3 electron interaction with formal bond order of 1/2 that exists between the singly occupied local-π orbital on H2 O+ and the doubly occupied local-π lone pair on an adjacent H2 O in a π-stacked configuration where these orbitals are favorably disposed for significant overlap. Early AIMD studies on ionization of small water clusters42,43 using gradient-corrected DFT fallaciously found hemibonded structures to be energetically preferred over protontransferred structures. In fact it has been found that many commonly used DFT methods fail to properly describe this and related systems, which behavior has been attributed to ACS Paragon 2 Plus Environment

Page 2 of 21

Page 3 of 21

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


arise from the self-interaction error.21,52 It has been shown that DFT can sometimes give qualitatively correct results on hemibonded water dimer cation if exact exchange is included in the functional,21,23,25,31,32,35 if explicit correction is made for the self-interaction error,24 if a long-range corrected functional is employed,34 or if constrained DFT calculations are used as a basis for a multiconfigurational valence bond method.30 Some AIMD studies on ionized water dimer cation that primarily focused on the proton transfer process have also noted the transient presence of hemibonded structures. One such study reported hemibonded structures in several trajectories49 and another study found hemibonded structures in one channel as a minor species on the way to dissociation.50 Calculations on water dimer cation have established that an intially produced vertically ionized water dimer can transfer a proton along a monotonically decreasing minimum energy path to reach the global minimum proton-transferred structure.16–18,20,24 The local minimum hemibonded structure must surmount a significant barrier to convert to the global minimum structure.19,25,26,34,50 No previous calculations have characterized details of how a vertically ionized water dimer might be converted to the hemibonded structure. The significant barrier to proton transfer suggests that if the hemibonded structure is once formed it might have a long enough lifetime to be an observable species. It could be formed in radiolysis of ordinary liquid water as an occasional alternative to the protontransfer channel. In irradiated water at low pH hemibonded cations could alternatively be formed by acid protonation of hydroxyl radicals. The present work uses coupled cluster electronic structure methods to provide a more complete and accurate characterization of the hemibonded water dimer cation. It is shown there is essentiallly no energetic hindrance to direct transformation of the vertically ionized water dimer to the hemibonded structure. The structural features that provide a unique signature of the hemibonded structure are noted for its possible identification in dynamical computations. Its optical absorption spectrum and its resonance Raman vibrational spectrum are also characterized. These results provide a foundation and benchmark for further studies on larger water cation clusters for the ultimate purpose of aiding possible identification of hemibonded cations in irradiated liquid water.



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

COMPUTATIONAL METHODS

Methods for doublet sysems based on CCSD54 can sometimes have significant spincontamination problems in the intermediate stages, regardless of whether unrestricted or restricted Hartree-Fock orbitals are used for the open-shell reference state. Such symmetry breaking difficulties are ameliorated with methods based on EOM-IP-CCSD,55–58 which utilizes a closed-shell reference state, and therefore Pieniezak et al.24 and Herr et al.39 have advocated the latter approach for water dimer cation calculations. Open-shell calculations were therefore done with EOM-IP-CCSD for ground state energies, geometries, gradients, and frequencies, and supplemented at selected points with the higher-level EOM-IP-CC(2,3)59,60 method for ground and excited state energies. Calculations on closed-shell species were done with CCSD for ground state energies, geometries, and frequencies and supplemented at selected points with EOM-CCSD61–63 and EOM-CC(2,3)59 methods for ground and excited state energies. The basis sets used include 6-311++G**64–66 and the considerably larger and more flexible aug-cc-pVTZ.67,68 Geometries of hemibonded and proton-transferred structures obtained from the EOMIP-CCSD/6-311++G** method previously reported in the literature24 were confirmed in this work. Geometries of all water dimer cations studied in the present work obtained from the EOM-IP-CCSD/aug-cc-pVTZ method are given in the Supporting Information. Electronic structure calculations were done with the QChem 4 program.69 The geometry optimizations were done with analytic gradient methods using tight convergence crtieria. Harmonic vibrational frequencies of the various normal modes were determined from numerical finite differences of the analytic gradients obtained at slightly displaced geometries. Locally developed programs were used to evaluate certain additional properties of vibrational modes, including total energy distributions,70 the anharmonic levels of a numerically-given 1D potential, and relative resonance Raman intensities. The latter were determined at the energies of several excited states with the formula71–75 ′

Ik ∝ (Vk )2 /ωk ′

which requires the vertical excited state gradient V projected onto the ground state normal mode k having frequency ωk . This formula is based on a number of simplifying approximations and is expected to mainly useful to identify the strongest lines in the spectrum. The relative intensities are arbitrarily normalized such that their sum over all modes is unity. ACS Paragon 4 Plus Environment

Page 4 of 21

Page 5 of 21


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


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 6 of 21

TABLE I: Salient intermolecular geometrical parameters of water dimer neutral and various cations as obtained with different methods. Distances in ˚ A and angles in degrees. Structure

EOM-IP-CCSD 6-311++G**

EOM-IP-CCSD

CCSD(T)a

aug-cc-pVTZ

aug-cc-pVQZ

R(O,O) V

2.938b

2.913b

H

2.050c

2.025

2.024

T

2.283

2.270

2.210

P

2.467c

2.470

2.506

Θ(W,W) V

90.0b

90.0b

H

12.4c

15.1

13.1

T

79.3

84.4

89.4

P

50.8c

51.1

53.7

a Parameters

from Reference 26. b Parameters for structure V are from CCSD calculations. c Parameters from Reference 24.

at the optimum geometry of neutral water dimer is denoted V , the global minimum cation proton-transferred structure is denoted P, the local minimum cation hemibonded structure is denoted H , and the transition state cation structure connecting H and P is denoted T . The relative energies and O-O distances of these structures are illustrated in Fig. 1, along with the viable connections among them. More detailed results on ground state geometries are given in Table 1, while energies are given in Table 2. In structure V the O-O distance is about 2.91 ˚ A and the two hydrogen bonded monomers lie in mutually perpendicular planes. The vertical cation of structure V requires about 23 kcal/mol to dissociate into H2 O+ and H2 O. Upon transferring a proton to the other oxygen TABLE II: Relative ground state energies in kcal/mol for water dimer cations as obtained with different methods.a . Structure

H2 O+ and H2 O asymptote H3

O+

and OH asymptote

EOM-IP-CCSD

EOM-IP-CC(2,3)

EOM-IP-CCSD

EOM-IP-CC(2,3)

CCSD(T)b

6-311++G**

6-311++G**

aug-cc-pVTZ

aug-cc-pVTZ

aug-cc-pVQZ

44.40

46.90

44.75

47.19

46.7 22.3

22.84

21.55

24.37

22.41

V

20.62

22.47

21.57

23.70

H

5.27

7.44

4.49

6.31

7.09

H (inc ZPE)c

6.61

8.96

6.01

7.83

8.84

T

12.93

16.24

13.23

14.70

15.14

P

0.00

0.00

0.00

0.00

0.00

a Energies

for H2 O and OH are from CCSD calculations.

b Energies

from reference 26.

c These

values include corrections for

zero-point vibrational (ZPE) energies. The ZPE corrections for EOM-IP-CC(2,3) are from EOM-IP-CCSD calculations.


Page 7 of 21

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


atom the O-O distance is shortened to about 2.47 ˚ A and is stabilized without barrier by about 24 kcal/mol to structure P. Structure P requires about 22 kcal/mol to dissociate into H3 O+ and OH. Alternatively, the cation of structure V can be stabilized by about 17 kcal/mol to form structure H . Conversion of the latter to structure P would give about 6 kcal/mol of further stabilization (which value becomes about 8 kcal/mol if zero point vibrational energies are included). However this requires first surmounting a significant energy barrier of about 8 kcal/mol to reach structure T . A normal mode calculation carried out on structure T at the EOM-IP-CCSD/6311++G** level verified it as a true transition state by virtue of having exactly one imaginary frequency. An intrinsic reaction coordinate mapped out at the EOM-IP-CCSD/6-311++G** level by following steepest descent paths in either direction from structure T along the imaginary frequency mode verified that structure T did indeed connect the H and P minima and that no local bumps exist on the paths. Structure H is notably characterized by its very short O-O distance of about 2.02 ˚ A and by the approximately parallel relative orientation of the two monomer planes, which make an angle Θ(W,W) of about 15◦ with one another. Taken together these two characteristics provide a unique and convenient signature for identification of hemibonded structures that may be present in dynamical calculations. The EOM-IP-CCSD/aug-cc-pVTZ and CCSD(T)/aug-cc-pVQZ26 methods show the ground state to have symmetry 2 B in the C2 point group. The EOM-IP-CCSD/6-311++G** method shows a very slight geometry change and energy lowering of just 0.005 kcal/mol upon relaxing from C2 to C1 symmetry. Paths leading the water dimer cation from structure V to structure H have not previously been reported. This matter was first investigated with a linear synchronous transit (LST) in internal (z-matrix) coordinates, where all such coordinates are stepped from their initial to final values by a common factor of x that ranges from 0 to 1 in increments of 0.05. This path shows a small bump at x∼0.35 of 0.7 kcal/mol with EOM-IP-CCSD/6-311++G** and 0.5 kcal/mol with EOM-IP-CCSD/aug-cc-pVTZ. Brief exploration indicated that a more facile path could be obtained by a modification of the LST path in which most of the change in the tilting angle of the proton donor monomer plane with respect to the O-O bond is delayed until somewhat later in the transit. Thus, an alternative path was constructed in which most coordinates were given a strict LST treatment, being changed from their initial to final values ACS Paragon 7 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

Page 8 of 21

TABLE III: Vertical excitation energies in eV (and oscillator strengths in parentheses) for structure H obtained with different methods.a The ground state has 2 B symmetry in the C2 point group.b state symmetry

EOM-IP-CCSD

EOM-IP-CC(2,3)

EOM-IP-CCSD

EOM-IP-CC(2,3)

6-311++G**

6-311++G**

aug-cc-pVTZ

aug-cc-pVTZ

2A

3.36 (0.16)

3.36

3.36 (0.14)

3.36

2B

5.01 (0.00)

5.01

4.97 (0.00)

4.98

2A

5.11 (0.20)

5.09

5.06 (0.20)

5.04

a Geometries

for EOM-IP-CC(2,3) are from EOM-IP-CCSD calculations.

b The

EOM-IP-CCSD/6-311++G** geometry is

strictly in the C1 point group, but the distortion from C2 is very small so the states are labelled by their proximity to those of the latter, thereby providing consistent labelling with the results found with the EOM-IP-CCSD/aug-cc-pVTZ geometry.

by the linear factor x, while changes in the tilting angle of the proton donor monomer plane with respect to the O-O bond were instead changed by a factor of x4 . This produced a path with a negligible bump of 0.01 kcal/mol with EOM-IP-CCSD/6-311++G** and no bumps at all with EOM-IP-CCSD/aug-cc-pVTZ, thereby demonstrating an essentially monotonic drop in energy throughout the entire conversion. It seems very likely that more elaborate exploration would identify many even more facile paths. However, even this brief sally is sufficient to draw the important qualitative conclusion that there is essentially no energetic hindrance to direct conversion of the water dimer cation from the optimum geometry of the neutral water dimer to the hemibonded structure.

Hemibonded Excited States

Time-resolved optical absorption spectroscopy has been a valuable experimental tool to identify transient species in solution.76,77 In this connection, vertical excitation energies of structure H are reported in Table 3. Three states are found in the near-UV region, at about 3.36 eV (369 nm), 4.98 eV (249 nm), and 5.04 eV (246 nm). The only related literature reports are a CIS/6-311++G(d,p) calculation53 giving the lowest excited state energy at 3.59 eV (345 nm), which is somewhat higher in energy than our analgous result, and a CCSD/aug-cc-pVDZ trajectory calculation49 that reported hemibonded structures in several trajectories which, using SAC-CI/aug-cc-pVDZ for excitation energies, gave strong UV absorption to the red side of 220 nm, which is in broad agreement with our results. The first and third of these near-UV excited states have very high oscillator strengths of about 0.14 and 0.20, respectively. The second state has a very low oscillator strength ACS Paragon 8 Plus Environment

Page 9 of 21

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 IV: Harmonic frequencies in cm−1 and relative resonance Raman intensities for the vibrations of structure H with different methods. Mode

Ground State Frequency (and Intensitiesa in 3 Excited States)

symmetry

EOM-IP-CCSD

EOM-IP-CCSD

CCSD(T)b

6-311++G**

aug-cc-pVTZ

aug-cc-pVQZ

intermolecular modes rock

A

67 (0.00,0.11,0.00)

94 (0.00,0.15,0.00)

67

W-W stretch

A

472 (0.50,0.48,0.58)

488 (0.52,0.49,0.58)

481

wag

B

553 (0.00,0.00,0.00)

585 (0.00,0.00,0.00)

631

twist

A

626 (0.00,0.00,0.01)

633 (0.00,0.00,0.01)

637

twist

B

644 (0.00,0.00,0.00)

654 (0.00,0.00,0.00)

653

wag

A

839 (0.45,0.14,0.21)

810 (0.42,0.10,0.26)

804

HOH bend

B

1583 (0.00,0.00,0.00)

1590 (0.00,0.00,0.00)

1585

intramolecular modes

HOH bend

A

1618 (0.05,0.28,0.19)

1617 (0.06,0.26,0.14)

1611

OH stretch

B

3632 (0.00,0.00,0.00)

3619 (0.00,0.00,0.00)

3594

OH stretch

A

3696 (0.00,0.00,0.01)

3678 (0.00,0.00,0.01)

3638

OH stretch

A

3767 (0.00,0.00,0.00)

3744 (0.00,0.00,0.00)

3711

OH stretch

B

3767 (0.00,0.00,0.00)

3747 (0.00,0.00,0.00)

3713

a Relative

resonance Raman intensities in each excited state are arbitrarily normalized to make the sum over all modes unity. Such intensities of 0.05 or larger are given in bold face. b Frequencies from Reference 26.

of 0.0001, but it may be able to borrow significant intensity through vibronic coupling to the nearby third excited state. Such high oscillator strengths for at least two of the excited states give encouragement that it might be possible to identify the hemibonded cation in irradiated bulk water by observation of its UV absorption spectrum.

Hemibonded Vibrations

Time-resolved resonance Raman spectroscopy has been another valuable experimental tool to identify transient species in solution.78 The very high oscillator strengths found for two of the near-UV transitions of structure H provided motivation to compute the ground state vibrational normal modes and to their estimate their relative resonance Raman intensities. Harmonic results are given in Table 4. The lowest six modes are mainly intermolecular in nature while the highest six modes are essentially intramolecular modes. Agreement between EOM-IP-CCSD/6-311++G**, EOM-IP-CCSD/aug-cc-pVTZ, and CCSD(T)/aug-cc-pVQZ frequencies is fair, the largest discrepancies being in the third lowest and third highest modes. An additional related ACS Paragon 9 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

Page 10 of 21

TABLE V: Harmonic and anharmonic frequencies of the W-W stretch mode obtained with different methods. level

harmonic

harmonic

anharmonic

anharmonic

EOM-IP-CCSD

EOM-IP-CCSD

EOM-IP-CCSD

EOM-IP-CCSD

6-311++G**

aug-cc-pVTZ

6-311++G**

aug-cc-pVTZ

fundamental

472

488

463

479

first overtone

944

976

917

948

second overtone

1417

1465

1361

1407

third overtone

1889

1953

1796

1857

literature report53 is a BHHLYP/6-311++G** calculation giving the second lowest mode at 465 cm−1 , which is somewhat lower than our best result. The EOM-IP-CCSD/6-311++G** and EOM-IP-CCSD/aug-cc-pVTZ relative resonance Raman intensities all agree well with one another, being within 0.05 in all cases. The modes showing significant relative resonance Raman intensity include the rock at roughly 90 cm−1 in the second excited state, and in all three excited states the W-W stretch at about 490 cm−1 , a wag at about 810 cm−1 , and a HOH bend at about 1620 cm−1 . The W-W stretch (aka the O-O stretch) is predicted to have the highest relative intensity in all three excited states and hence is the most likely to be observed with resonance Raman spectroscopy. We have therefore further investigated its anharmonicity. A total energy distribution analysis70 indictates that this mode comes within 1% of being a pure W-W stretching local mode, that is the two monomers approach and separate with very little change in internal structure or relative orientation. Taking advantage of this, onedimensional scans using EOM-IP-CCSD methods were made of the energy obtained by compressing and stretching just the O-O distance while keeping all other internal z-matrix coordinates fixed and numerically solving the associated 1D Schrödinger equation for the corresponding vibrational levels. Results are given in Table 5. Anharmonic corrections to the harmonic values, which are very nearly the same in both EOM-IP-CCSD/6-311++G** and EOM-IP-aug-cc-pVTZ calculations, are found to be significant, being about −9 cm−1 in the fundamental, −28 cm−1 in the first overtone, −57 cm−1 in the second overtone, and −95 cm−1 in the third overtone.

ACS Paragon10 Plus Environment

Page 11 of 21

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


CONCLUSION

This work has provided high-level computational results for the structures and relative energies of various forms of water dimer cation, including the vertically ionized neutral water dimer V , the local minimum hemibonded form H , the global minimum proton-transferred form P, and the transition state T connecting the latter two. It is pointed out that the presence of hemibonded forms in trajectory studies of ionized water clusters or liquid could be easily detected by searching for the combination of a very short O-O distance as low as 2.0 ˚ A and a near parallel relative orientation of the two participating monomers. It has been shown that a path of monotonically decreasing energy for the cation connects structure V with structure H , indicating that ionization of a neutral water dimer can directly lead to formation of the hemibonded structure as an energetically facile alternative to the minimum energy path that leads to the proton-transferred structure. The optical absorption spectrum of structure H has been predicted, finding very high oscillator strengths for two of the the three lowest excited states that all lie in the near-UV region. Relative resonance Raman spectrum intensities have also been estimated for structure H , finding that the W-W stretch is the most strongly enhanced mode in each of the excited states examined. Additionally, the anharmonicity and overtones of this mode have been evaluated. These results on the simple model system of water dimer cation establish a foundation for understanding of what may be expected for the possibility of observing hemibonded cations in the radiolysis of bulk water. The finding of a facile path of monotonically decreasing energy to form the hemibonded structure from a vertically ionized neutral water dimer indicates that hemibonded cations could be formed to some extent in radiolysis of ordinary water as an alternative channel competing with proton-transfer. In radiolysis of water at low pH the hemibonded structure could also be formed by acid protonation of hydroxyl radical. Once formed, the significant barrier preventing further conversion to the protontransferred structure indicates that the hemibonded cation may have a sufficient lifetime to be amenable to direct observation by time resolved optical absorption and/or resonance Raman spectroscopy. The predictions of these spectra for the hemibonded dimer cation obtained in this work provide clues about the spectroscopic signatures to be expected in any such experimental investigation. Analogous studies on larger water cation clusters are, of course, needed to make more ACS Paragon11 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

definitive connections to water cations that may be present in the condensed phase. In that connection the present results should be useful as benchmarks to validate more efficient computational methods that could readily be applied to such larger clusters.

ACKNOWLEDGEMENT

Dr. I. Janik is gratefully acknowledged for suggesting this study and for providing helpful discussions. This work is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under award number DE-FC02-04ER15533. This is manuscript number 5139 of the Notre Dame Radiation Laboratory. This work is also supported in part by the Notre Dame Center for Research Computing.

SUPPORTING INFORMATION

Geometries of all water dimer cations studied in the present work obtained from the EOM-IP-CCSD/aug-cc-pVTZ method.

REFERENCES

∗

Electronic address: [email protected]

1

Draganic, I. G.; Draganic, Z. D. The Radiation Chemistry of Water ; Academic Press: New York, 1971.

2

Spinks, J. W. T.; Woods, R. J. An Introduction to Radiation Chemistry; Wiley-Interscience: New York, 1990.

3

Garrett, B. C.; Dixon, D. A.; Camaioni, D. M.; Chipman, D. M.; Johnson, M. A.; Jonah, C. D.; Kimmel, G. A.; Miller, J. H.; Rescigno, T. N.; Rossky, P. J.; et al. Role of Water in ElectronInitiated Processes and Radical Chemistry: Issues and Scientific Advances. Chem. Rev. 2005, 105, 355–390.

4

Ogura, H.; Hamill, W. H. Positive hole migration in pulse-irradiated water and heavy water. J. Phys. Chem. 1973, 77, 2952–2954. ACS Paragon12 Plus Environment

Page 12 of 21

Page 13 of 21

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

Li, J.; Nie, Z.; Zheng, Y. Y.; Dong, S.; Loh, Z.-H. Elementary Electron and Ion Dynamics in Ionized Liquid Water. J. Phys. Chem. Lett. 2013, 4, 3698–3703.

6

Marsalek, O.; Elles, C. G.; Pieniazek, P. A.; Pluhaˇrová, E.; VandeVondele, J.; Bradforth, S. E.; Jungwirth, P. Chasing charge localization and chemical reactivity following photoionization in liquid water. J. Chem. Phys. 2011, 135, 224510:1–14.

7

Ma, J.; Schmidhammer, U.; Pernot, P.; Mostafavi, M. Reactivity of the Strongest Oxidizing Species in Aqueous Solutions: The Short-Lived Radical Cation H2O*+. J. Phys. Chem. Lett. 2014, 5, 258–261.

8

Ma, J.; LaVerne, J. A.; Mostafavi, M. Scavenging the Water Cation in Concentrated Acidic Solutions. J. Phys. Chem. A 2015, 119, 10629–10636.

9

Ghalei, M.; Ma, J.; Schmidhammer, U.; Vandenborre, J.; Fattahi, M.; Mostafavi, M. Picosecond Pulse Radiolysis of Highly Concentrated Carbonate Solutions. J. Phys. Chem. B 2016, 120, 2434–2439.

10

Lampe, F. W.; Field, F. H.; Franklin, J. L. Reactions of Gaseous Ions. IV. Water. J. Am. Chem. Soc 1957, 79, 6132–6135.

11

Gardenier, G. H.; Johnson, M. A.; McCoy, A. B. Spectroscopic Study of the Ion-Radical H-Bond in H4O2+. J. Phys. Chem. A 2009, 113, 4772–4779.

12

Mizuse, K.; Kuo, J.-L.; Fujii, A. Structural trends of ionized water networks: Infrared spectroscopy of watercluster radical cations (H2O)n+ (n = 3-11). Chem. Sci. 2011, 2, 868–876.

13

Mizuse, K.; Fujii, A. Characterization of a Solvent-Separated Ion-Radical Pair in Cationized Water Networks: Infrared Photodissociation and Ar-Attachment Experiments for Water Cluster Radical Cations (H2O)n+ (n = 3–8). J. Phys. Chem. A 2013, 117, 929–938.

14

Lathan, W. A.; Curtiss, L. A.; Hehre, W. J.; Lisle, J. B.; Pople, J. A. Molecular Orbital Structures for Small Organic Molecules and Cations. Prog. Phys. Org. Chem. 1974, 11, 175– 261.

15

Sato, K.; Tomoda, S.; Kimura, K.; Iwata, S. Electronic and molecular structure of the water dimer cation. A theoretical study. Chem. Phys. Lett. 1983, 95, 579–583.

16

Curtiss, L. A. Ab initio molecular orbital calculations of the first two adiabatic ionizations of the water dimer. Chem. Phys. Lett. 1983, 96, 442–446.

17

Tomoda, S.; Kimura, K. Proton-transfer potential-energy surfaces of the water dimer cation (H2O)2+ in the 12A’ and 12A states. Chem. Phys. 1983, 82, 215–227. ACS Paragon13 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

18

Tomoda, S.; Kimura, K. Do we observe the “adiabatic” ionizations of the water dimer? An interpretation of the threshold ionization energy and the nature of the ionic states. Chem. Phys. Lett. 1984, 111, 434–438.

19

Gill, P. M. W.; Radom, L. Structures and stabilities of singly charged three-electron hemibonded systems and their hydrogen-bonded isomers. J. Amer. Chem. Soc. 1988, 110, 4931–4941.

20

Sodupe, M.; Oliva, A.; Bertran, J. Theoretical Study of the Ionization of the H2O-H2O, NH3H2O, and FH-H2O Hydrogen-Bonded Molecules. J. Amer. Chem. Soc. 1994, 116, 8249–8258.

21

Sodupe, M.; Bertran, J.; Rodr´ıguez-Santiago, L.; Baerends, E. J. Ground State of the (H2O)2+ Radical Cation: DFT versus Post-Hartree-Fock Methods. J. Phys. Chem. A 1999, 103, 166–170.

22

Novakovskaya, Y. V.; Stepanov, N. F. Small Charged Water Clusters: Cations. J. Phys. Chem. A 1999, 103, 3285–3288.

23

Ghanty, T. K.; Ghosh, S. K. Ab Initio CASSCF and DFT Investigations of (H2O)2+ and (H2S)2+: Hemi-Bonded vs Proton-Transferred Structure. J. Phys. Chem. A 2002, 106, 11815– 11821.

24

Pieniazek, P. A.; VandeVondele, J.; Jungwirth, P.; Krylov, A. I.; Bradforth, S. E. Electronic Structure of the Water Dimer Cation. J. Phys. Chem. A 2008, 112, 6159–6170.

25

Lee, H. M.; Kim, K. S. Water Dimer Cation: Density Functional Theory vs Ab Initio Theory. J. Chem. Theory Comp. 2009, 5, 976–981.

26

Cheng, Q.; Evangelista, F. A.; Simmonett, A. C.; Yamaguchi, Y.; Schaefer III, H. F. Water Dimer Radical Cation: Structures, Vibrational Frequencies, and Energetics. J. Phys. Chem. A 2009, 113, 13779–13789.

27

Do, H.; Besley, N. A. Proton transfer or hemibonding? The structure and stability of radical cation clusters. Phys. Chem. Chem. Phys. 2013, 15, 16214–16219.

28

Do, H.; Besley, N. A. Structure and Bonding in Ionized Water Clusters. J. Phys. Chem. A 2013, 117, 5385–5391.

29

Stein, T.; Jiménez-Hoyos, C. A.; Scuseria, G. E. Stability of Hemi-Bonded vs Proton-Transferred Structures of (H2O)2+, (H2S)2+, and (H2Se)2+ Studied with Projected Hartree–Fock Methods. J. Phys. Chem. A 2014, 118, 7261–7266.

30

Rapacioli, M.; Spiegelman, F.; Scemama, A.; Mirtschink, A. Modeling Charge Resonance in Cationic Molecular Clusters: Combining DFT-Tight Binding with Configuration Interaction. J. Chem. Theory Comp. 2011, 7, 44–55. ACS Paragon14 Plus Environment

Page 14 of 21

Page 15 of 21

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


31

Livshits, E.; Granot, R. S.; Baer, R. A Density Functional Theory for Studying Ionization Processes in Water Clusters. J. Phys. Chem. A 2011, 115, 5735–5744.

32

Lee, H. M.; Kim, K. S. Water trimer cation. Theor. Chem. Acc. 2011, 130, 543–548.

33

Segarra-Mart´ı, J.; Merch´ an, M.; Roca-Sanju´ an, D. Ab initio determination of the ionization potentials of water clusters (H2O)n (n = 26). J. Chem. Phys. 2012, 136, 244306:1–11.

34

Pan, P.-R.; Lin, Y.-S.; Tsai, M.-K.; Kuo, J.-L.; Chai, J.-D. Assessment of density functional approximations for the hemibonded structure of the water dimer radical cation. Phys. Chem. Chem. Phys. 2012, 14, 10705–10712.

35

Lee, H. M.; Kim, K. S. Dynamics and structural changes of small water clusters on ionization. J. Comp. Chem. 2013, 34, 1589–1597.

36

Lu, E.-P.; Pan, P.-R.; Li, Y.-C.; Tsai, M.-K.; Kuo, J.-L. Structural evolution and solvation of the OH radical in ionized water radical cations (H2O)n+, n = 5-8. Phys. Chem. Chem. Phys. 2014, 16, 18888–18895.

37

Lv, Z.-L.; Xu, K.; Cheng, Y.; Chen, X.-R.; Cai, L.-C. Ab initio investigation of the lower energy candidate structures for (H2O)5+ water cluster. J. Chem. Phys. 2014, 141, 054309:1–8.

38

Lv, Z.-L.; Cheng, Y.; Chen, X.-R.; Cai, L.-C. Structural exploration and properties of cluster via ab initio in combination with particle swarm optimization method. Chem. Phys. 2015, 452, 25–30.

39

Herr, J. D.; Talbot, J.; Steele, R. P. Structural Progression in Clusters of Ionized Water, (H2O)n=1–5+. J. Phys. Chem. A 2015, 119, 752–766.

40

Talbot, J. J.; Cheng, X.; Herr, J. D.; Steele, R. P. Vibrational Signatures of Electronic Properties in Oxidized Water: Unraveling the Anomalous Spectrum of the Water Dimer Cation. J. Amer. Chem. Soc. 2016, 138, 11936–11945.

41

Herr, J. D.; Steele, R. P. Ion–Radical Pair Separation in Larger Oxidized Water Clusters, (H2O)+n=6–21. J. Phys. Chem. A 2016, 120, 7225–7239.

42

Barnett, R. N.; Landman, U. Pathways and Dynamics of Dissociation of Ionized (H2O)2. J. Phys. Chem. 1995, 99, 17305–17310.

43

Barnett, R. N.; ; Landman, U. Structure and Energetics of Ionized Water Clusters: (H2O)n+, n = 2–5. J. Phys. Chem. A 1997, 101, 164–169.

44

Tachikawa, H. A Direct ab–Initio Trajectory Study on the Ionization Dynamics of the Water Dimer. J. Phys. Chem. A 2002, 106, 6915–6921. ACS Paragon15 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

45

Tachikawa, H. Ionization Dynamics of the Small–Sized Water Clusters: A Direct Ab Initio Trajectory Study. J. Phys. Chem. A 2004, 108, 7853–7862.

46

Furuhama, A.; Dupuis, M.; Hirao, K. Reactions associated with ionization in water: A direct ab initio dynamics study of ionization in (H2O)17. J. Chem. Phys. 2006, 124, 164310:1–10.

47

Furuhama, A.; Dupuis, M.; Hirao, K. Application of a kinetic energy partitioning scheme for ab initio molecular dynamics to reactions associated with ionization in water tetramers. Phys. Chem. Chem. Phys. 2008, 10, 2033–2042.

48

Kamarchik, E.; Kostko, O.; Bowman, J. M.; Ahmed, M.; Krylov, A. I. Spectroscopic signatures of proton transfer dynamics in the water dimer cation. J. Chem. Phys. 2010, 132, 194311:1–11.

49

Tsai, M.-K.; Kuo, J.-L.; Lu, J.-M. The dynamics and spectroscopic fingerprint of hydroxyl radical generation through water dimer ionization: ab initio molecular dynamic simulation study. Phys. Chem. Chem. Phys. 2012, 14, 13402–13408.

50

Svoboda, O.; Hollas, D.; Oncak, M.; Slavicek, P. Reaction selectivity in an ionized water dimer: nonadiabatic ab initio dynamics simulations. Phys. Chem. Chem. Phys. 2013, 15, 11531–11542.

51

Tachikawa, H.; Takada, T. Proton transfer rates in ionized water clusters (H2O)n (n = 2-4). RSC Adv. 2015, 5, 6945–6953.

52

Gr¨ uning, M.; Gritsenko, O. V.; van Gisbergen, S. J. A.; Baerends, E. J. The Failure of Generalized Gradient Approximations (GGAs) and Meta-GGAs for the Two-Center Three-Electron Bonds in He2+, (H2O)2+, and (NH3)2+. J. Phys. Chem. A 2001, 105, 9211–9218.

53

Maity, D. K. Sigma Bonded Radical Cation Complexes: A Theoretical Study. J. Phys. Chem. A 2002, 106, 5716–5721.

54

Dalgaard, E.; Monkhorst, H. J. Some aspects of the time-dependent coupled-cluster approach to dynamic response functions. Phys. Rev. A 1983, 28, 1217–1222.

55

Sinha, D.; Mukhopadhyay, S.; Mukherjee, D. A note on the direct calculation of excitation energies by quasi-degenerate MBPT and coupled-cluster theory. Chem. Phys. Lett. 1986, 129, 369–374.

56

Sinha, D.; Mukhopadhyay, S.; Chaudhuri, R.; Mukherjee, D. The eigenvalue-independent partitioning technique in Fock space: An alternative route to open-shell coupled-cluster theory for incomplete model spaces. Chem. Phys. Lett. 1989, 154, 544–549.

57

Chaudhuri, R.; Mukhopadhyay, D.; Mukherjee, D. Applications of open-shell coupled cluster theory using an eigenvalue-independent partitioning technique: Approximate inclusion of triples ACS Paragon16 Plus Environment

Page 16 of 21

Page 17 of 21

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


in IP calculations. Chem. Phys. Lett. 1989, 162, 393–398. 58

Stanton, J. F.; Gauss, J. A simple scheme for the direct calculation of ionization potentials with coupled-cluster theory that exploits established excitation energy methods. J. Chem. Phys. 1999, 111, 8785–8788.

59

Hirata, S.; Nooijen, M.; Bartlett, R. J. High-order determinantal equation-of-motion coupledcluster calculations for ionized and electron-attached states. Chem. Phys. Lett. 2000, 328, 459– 468.

60

Manohar, P. U.; Stanton, J. F.; Krylov, A. I. Perturbative triples correction for the equation-ofmotion coupled-cluster wave functions with single and double substitutions for ionized states: Theory, implementation, and examples. J. Chem. Phys. 2009, 131, 114112:1–13.

61

Stanton, J. F.; Bartlett, R. J. The equation of motion coupled-cluster method. A systematic biorthogonal approach to molecular excitation energies, transition probabilities, and excited state properties. J. Chem. Phys. 1993, 98, 7029–7039.

62

Krylov, A. I. Equation-of-motion coupled-cluster methods for open-shell and electronically excited species: The Hitchhiker’s guide to Fock space. Ann. Rev. Phys. Chem. 2008, 59, 433–462.

63

Bartlett, R. J. Coupled-cluster theory and its equation-of-motion extensions. WIREs Comput. Mol. Sci. 2012, 2, 126–138.

64

Hehre, W. J.; Ditchfield, R.; Pople, J. A. Self–Consistent Molecular Orbital Methods. XII. Further Extensions of Gaussian–Type Basis Sets for Use in Molecular Orbital Studies of Organic Molecules. J. Chem. Phys. 1972, 56, 2257–2261.

65

Hariharan, P. C.; Pople, J. A. The influence of polarization functions on molecular orbital hydrogenation energies. Theor. Chim. Acta 1973, 28, 213–222.

66

Clark, T.; Chandrasekhar, J.; Spitznagel, G. W.; Schleyer, P. V. R. Efficient diffuse functionaugmented basis sets for anion calculations. III. The 3-21+G basis set for first-row elements, Li–F. J. Comp. Chem. 1983, 4, 294–301.

67

Dunning, T. H. Gaussian basis sets for use in correlated molecular calculations. 1. The atoms boron through neon and hydrogen. J. Chem. Phys. 1989, 90, 1007–1023.

68

Kendall, R. A.; Dunning, 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.

69

Shao, Y.; Gan, Z.; Epifanovsky, E.; Gilbert, A. T. B.; Wormit, M.; Kussmann, J.; Lange, A.; Behn, A.; Deng, J.; Feng, X.; et al. Advances in molecular quantum chemistry contained in the ACS Paragon17 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

Q-Chem 4 program package. Mol. Phys. 2015, 184–215. 70

Pulay, P.; Torok, F. On Parameter Form of Matrix F. 2. Investigation of Assignment with Aid of Parameter Form. Act. Chim. Hung. 1966, 47, 273–279.

71

Heller, E. Potential Surface Properties and Dynamics from Molecular Spectra: A TimeDependent Picture. In Potential Energy Surfaces and Dynamics Calculations; Truhlar, D., Ed.; Plenum, New York, 1981; Chap. 4, pp 103–131.

72

Heller, E. J.; Sundberg, R.; Tannor, D. Simple aspects of Raman scattering. J. Phys. Chem. 1982, 86, 1822–1833.

73

Morris, D. E.; Woodruff, W. H. Detailed aspects of Raman scattering. Overtone and combination intensities and prescriptions for determining excited-state structure. J. Phys. Chem. 1985, 89, 5795–5798.

74

Lee, S.-Y.; Mathies, R. A. Polarizability theory and sum rules. Chem. Phys. Lett. 1988, 151, 9–15.

75

Ling, S.; Imre, D. G.; Heller, E. J. Effects of the transition dipole in Raman scattering. J. Phys. Chem. 1989, 93, 7107–7119.

76

Patterson, L. K.; Lilie, J. A computer-controlled pulse radiolysis system. Int. J. Rad. Phys. Chem. 1974, 6, 129–141.

77

Janata, E.; Schuler, R. H. Rate constant for scavenging eaq- in nitrous oxide-saturated solutions. J. Phys. Chem. 1982, 86, 2078–2084.

78

Tripathi, G. N. R. Time-resolved resonance Raman spectroscopy of chemical reaction intermediates in solution. In Advances in Spectroscopy, Vol. 18, Time-resolved Spectroscopy; Clark, R. J. H., Hester, R. E., Eds.; John Wiley and Sons, 1989; Vol. 18; Chapter 4, pp 157–218.

ACS Paragon18 Plus Environment

Page 18 of 21

Page 19 of 21


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


50

H2O+ ... H2O

40

E (kcal/mol)

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

Page 20 of 21

30

V

H3O+ ... OH

20

T 10

0

H P 2.0

2.5

3.0

R(O-O) (Å)

ACS Paragon Plus Environment

∞

Page 21 of 21

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


ACS Paragon Plus Environment

Hemibonding between Water Cation and Water - The Journal of

Recommend Documents