Ab Initio Calculations of the Structure, Kinetics, and Infrared Laser Chemical Reaction Dynamics of Fluorooxirane

Ha, Tae–Kyu; Pochert, Jörg; Qüack, Martin

doi:10.1021/jp9801222

Cited by 4 publications

(22 citation statements)

References 29 publications

(67 reference statements)

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“…HI-MO vibrational spectra 11 computed for seven isotopomers of CB were shown to correlate well with the observed IR/Raman transitions of Ar/CB, except for a specific set of vibrations showing pronounced anharmonic perturbations associated with the double-well PES of CB. As has already been noted, 11 supporting evidence for the success of computations at a level equivalent to HI-MO is provided by recent computationalexperimental research on fluorooxirane, 12,13 a strained ring molecule with a single deep PES minimum. The present computational work includes both full and specifically constrained geometry optimizations on the CB:Ar n and Ar n clusters chosen for study, along with numerous single point energy computations.…”

Section: Mo Computational Procedures and Introductory Resultsmentioning

confidence: 75%

“…His research stimulated experimental [2][3][4] and theoretical [5][6][7][8][9][10] work aimed at characterizing the process and recent results 11 identified nonautomerizing, as well as automerizing, vibrational state-specific and isotopomer-specific anharmonic spectroscopic behavior. The zero-point energy level splitting for gaseous 12 C 4 H 4 was estimated to be near 11 cm -1 to suggest a ZP tunneling rate verging on the picosecond time scale. The analysis combined (a) the vibrational spectra of low-temperature matrixisolated CB isotopomers obtained by Arnold and Michl; 3 (b) the twenty configuration MCSCF/6-31G MO computation of the square-planar CB saddle-point by Nakamura et al; 7 (c) MOcomputed vibrational spectra for CB isotopomers at the MP2/ 6-311++G(2d,2p) level [here called HI-MO]; and (d) computed 1-D PES profiles for 12 C 4 H 4 along automerization coordinates originating as the CdC stretching normal mode.…”

Section: Introductionmentioning

confidence: 99%

“…The zero-point energy level splitting for gaseous 12 C 4 H 4 was estimated to be near 11 cm -1 to suggest a ZP tunneling rate verging on the picosecond time scale. The analysis combined (a) the vibrational spectra of low-temperature matrixisolated CB isotopomers obtained by Arnold and Michl; 3 (b) the twenty configuration MCSCF/6-31G MO computation of the square-planar CB saddle-point by Nakamura et al; 7 (c) MOcomputed vibrational spectra for CB isotopomers at the MP2/ 6-311++G(2d,2p) level [here called HI-MO]; and (d) computed 1-D PES profiles for 12 C 4 H 4 along automerization coordinates originating as the CdC stretching normal mode. The analysis smoothly melded the patently nonharmonic Raman transitions observed at 723 and 1678 cm -1 for Ar/CB matrix samples with the low MO-computed 7 value of 3.2 kcal/mol (1119 cm -1 ) for the ZPE-corrected saddle-point energy of D 4h CB.…”

Section: Introductionmentioning

confidence: 99%

“…No spectroscopic tunneling doublets were observed; however, IR polarization measurements 3 and 13 C-NMR line shape analysis 2 of vicinally 13 C-dilabeled CB isolated in Ar suggested an automerization rate g 10 3 s -1 , i.e., a rate for these matrix-isolated isotopomers that is fast on the time scale of the NMR experiments. Computations by Carsky and Michl 10 for the vibrational state-specific tunneling splittings of the three lowest-frequency vibrations with a g symmetry species were based on an MO-computed PES with an automerization barrier of about 10 kcal/mol, and on this basis the tunneling splitting for the automerization fundamental of gaseous 12 C 4 H 4 was estimated to be 70 cm -1 . Carsky and Michl 10 addressed the failure to observe spectroscopic tunneling structure 4 for CB isolated in Ar or Ne by suggesting that CB and its matrix trapping site are unlikely to have the same symmetry properties.…”

Section: Introductionmentioning

confidence: 99%

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Ab Initio Modeled Matrix Trapping Sites, PES Asymmetry, and Automerization in the Ar/Cyclobutadiene System

Redington

2000

J. Phys. Chem. A

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The symmetrical geometries of 1,3-cyclobutadiene (CB) and substitutional vacancies in crystalline fcc Ar allow purely ab initio MO estimations to be made for the stabilization energies of several symmetric trapping sites in the Ar/CB matrix system at the MP2/6-311++G(2d,2p) [denoted HI-MO] level of theory. The single-substitutional vacancy supports the most stable trapping site in the HI-MO Ar/CB system. It was examined by filling an Ar13 vacancy of the HI-MO Ar lattice with a symmetrical CB:Ar12 kernel cluster, with dilation of the kernel cluster opposed by a symmetrical HI-MO lattice distortion PEF derived for the purpose. In addition, various supplemental HI-MO stabilization energies were computed. Slightly displacing the four nearest-neighbor Ar atoms coplanar with CB from square-planar geometry shows this site distortion PEF is very soft. The results suggest fluxional behavior for the Ar atoms near the CB guest molecule and the soft trapping site environment provides access to equivalent global PES minima for the two valence isomers of CB. The fast automerization coordinate of CB acts in the presence of slow lattice coordinates to account for the unique spectroscopic observations on Ar/CB reported from the laboratories of J. Michl. These show (a) that CB automerizes at a rate ≥ 103 s-1 in cold matrices; (b) that equal populations exist for the matrix-isolated vicinally dilabeled (13C or D) CB valence isomers; and (c) that the automerization ZP energy levels of matrix-isolated CB are separated by an amount Δ ≥ 35 cm-1. Trapping sites for CB based on multiple Ar vacancies are not only computed to be less stable than the SS site, but they are unable to support a satisfactory explanation for the experimental observations.

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Section: Mo Computational Procedures and Introductory Resultsmentioning

confidence: 75%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Ab Initio Modeled Matrix Trapping Sites, PES Asymmetry, and Automerization in the Ar/Cyclobutadiene System

Redington

2000

J. Phys. Chem. A

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“…As well as the ketene product, several other products are equally possible but they have not been taken into consideration in ref. 11. Earlier theoretical investigations12h18 on the systems have mainly [C 2 H 3 FO] been conÐned to the conformational analysis and prediction of vibrational wavenumbers and thermochemical parameters.…”

Section: Introductionmentioning

confidence: 99%

Potential energy surface for unimolecular dissociations and rearrangements of the ground state of [C2H3FO] systems

Nguyen¹,

Sumathi²,

Nguyen³

1999

Phys. Chem. Chem. Phys.

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The potential energy surface (PES) of systems in its electronic ground state has been investigated [C 2 H 3 FO] using density functional theory method, at the B3LYP/6-311]]G(d,p) level. Ten stable intermediates, including acetyl Ñuoride (1), Ñuoroacetaldehyde (9), 1-Ñuorovinyl alcohol (4), 2-Ñuorovinyl alcohol, carbenes and Ñuorooxiranes, have been located. Most stationary points on the PES corresponding to the molecular elimination and rearrangement channels from these intermediates have been identiÐed. Ketene ( 8) is found to be the predominant product in the unimolecular dissociations of 1, 4, 9 and Ñuorooxirane (6). The most probable channels for ketene formation from acetyl Ñuoride are 1 ] 8 and 1 ] 4 ] 8. In the reactions of both and radicals, both these processes are energetically feasible for the thermal reactants and CH 3 CO~Fh ence should lead to a spontaneous emission of vibrationally hot HF. The present PES characterises the reaction to be a capture-limited associationÈelimination reaction with a very high and CH3 CO~] Fp ressure-independent rate coefficient. In addition to its direct decomposition to ketene, 9 can give rise to stable rearrangement products, viz., 2-Ñuorovinyl alcohol (12) and 6. Fluorooxirane (6) decomposes to ketene through its isomerisation to 9 as intermediate and the present study provides an explanation for the non-observation of this intermediate.

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State-specific vibrational anharmonicities in cyclobutadiene and evidence for fast automerization by C412H4

Redington

1998

The Journal of Chemical Physics

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MO computations of vibrational spectra for 1,3-cyclobutadiene (CB) and CB:CO2 van der Waals molecule isotopomers at the MP2/6-311++G(2d,2p) level of MO theory are analyzed together with the extensive Ar/CB matrix-isolation spectra of the Michl group, the low 3.2 kcal/mol (ZPE-corrected) MO-computed energy of the square-planar saddle-point for CB reported by Nakamura et al., and opportune one-dimensional analysis of the automerization energy levels of C412H4. The composite interpretation results in the assignment of the strongly anharmonic Raman transitions of Ar/CB observed at 723 and 1678 cm−1 to the E2-E0 and E4-E0 transitions, respectively, in the automerization coordinate. The C13 and D isotope dependencies of the nominal C=C stretching and δCH wagging vibrational normal modes of the CB valence isomers depend markedly on whether the labeled HC=CH moieties of CB are mass equivalent or not, and the pronounced normal mode differences are viewed as providing different gateways into the global anharmonic PES domains. The automerization coordinate Qa originates as the nominal C=C stretching normal coordinate of ag symmetry, followed by a curving to more efficiently interchange the C=C and C–C bond lengths as the square-planar D4h configuration is approached. The latter is crossed at a geometry dilated with respect to the saddle-point, thereby providing a barrier configuration about 5 kcal/mol above the PES minima (i.e., a dilation energy of about 2 kcal/mol plus the 3.2 kcal/mol saddle-point energy). The computed zero-point levels of C412H4 (1-D modeling) are separated by E1-E0=11 cm−1 to suggest ZP tunneling rates reaching the picosecond time scale. The analysis exposes new aspects of the intramolecular dynamics of CB, and the proposed automerization mechanism accounts for all of the presently known information pertaining to this interesting property of the cyclobutadiene molecule.

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Ab Initio Calculations of the Structure, Kinetics, and Infrared Laser Chemical Reaction Dynamics of Fluorooxirane

Cited by 4 publications

References 29 publications

Ab Initio Modeled Matrix Trapping Sites, PES Asymmetry, and Automerization in the Ar/Cyclobutadiene System

Ab Initio Modeled Matrix Trapping Sites, PES Asymmetry, and Automerization in the Ar/Cyclobutadiene System

Potential energy surface for unimolecular dissociations and rearrangements of the ground state of [C2H3FO] systems

State-specific vibrational anharmonicities in cyclobutadiene and evidence for fast automerization by C412H4

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