Theoretical studies of the electronic spectrum of thioformaldehyde

Burton, Peter G.; Peyerimhoff, Sigrid D.; Buenker, Robert J.

doi:10.1016/0301-0104(82)85151-3

Cited by 33 publications

(22 citation statements)

References 58 publications

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“…However, substantial bodies of photochemical, photophysical, and spectroscopic evidence have been used to unequivocally establish that the electronic origins of the IT + IT* transitions are at least 20-30 kJ mol-' lower than those of the lowest (n + 4s) Rydbergs (1,(5)(6)(7). Subsequent large scale CI calculations (8) have resulted in a downward revision of the calculated '(IT, IT*) state energy in H2CS, consistent with this experimental evidence.…”

Section: Introductionmentioning

confidence: 79%

“…The assignment of the remaining two Rydberg transitions in the 200-210 nm region is less clear. Calculations predict the 'A2 (n, 4px), 'Al (n, 4py), and 'B2 (n, 4p,) states should have almost identical energies in small thiocarbonyls such as thioformaldehyde (8) and thioacetone (3,4). We rule out an 'A2 + %(lA1) assignment for either band system on the grounds that such a transition will be electric dipole forbidden in CZv (local) symmetry .- exhibits a weak D t x Rydberg transition at ca.…”

Section: Resultsmentioning

confidence: 99%

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Rydberg states in adamantanethione, thiofenchone, and thiocamphor

Falk¹,

Steer²

1988

Can. J. Chem.

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Section: Introductionmentioning

confidence: 79%

Section: Resultsmentioning

confidence: 99%

Rydberg states in adamantanethione, thiofenchone, and thiocamphor

Falk¹,

Steer²

1988

Can. J. Chem.

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“…where ∆E sd is the contribution of single and double excitations to the energy, and ∆E DC is the standard Davidson correction. For single-reference closed-shell configurations with at least four electrons, if the effects of quadruple excitations are assumed to be much larger than triple excitations, then the above formula for the Davidson correction (with an expected value of λ DC ∼ 0.5 for closed-shell He-H 2 ) can be derived theoretically [44][45][46][47] . We not only used multiple references, we also used open and mixed shell SCF cases; we therefore obtained values for the parameter λ DC by minimizing the average differences between MRD-CI energy values computed for the same point with different reference sets (which thus had different sizes for the Davidson correction).…”

Section: Small Corrections Applied To the Mrd-ci Energiesmentioning

confidence: 99%

Accurate analytic He–H2 potential energy surface from a greatly expanded set of ab initio energies

Boothroyd

Martín

Peterson

2003

The Journal of Chemical Physics

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The interaction potential energy surface (PES) of He-H 2 is of great importance for quantum chemistry, as the simplest test case for interactions between a molecule and a closed-shell atom. It is also required for a detailed understanding of certain astrophysical processes, namely collisional excitation and dissociation of H 2 in molecular clouds, at densities too low to be accessible experimentally. A new set of 23 703 ab initio energies was computed, for He-H 2 geometries where the interaction energy was expected to be nonnegligible. These have an estimated rms "random" error of ∼ 0.2 millihartree and a systematic error of ∼ 0.6 millihartree (0.4 kcal/mol). A new analytic He-H 2 PES, with 112 parameters, was fitted to 20 203 of these new ab initio energies (and to an additional 4862 points generated at large separations). This yielded an improvement by better than an order of magnitude in the fit to the interaction region, relative to the best previous surfaces (which were accurate only for near-equilibrium H 2 molecule sizes). This new PES has an rms error of 0.95 millihartree (0.60 kcal/mole) relative to the the 14 585 ab initio energies that lie below twice the H 2 dissociation energy, and 2.97 millihartree (1.87 kcal/mole) relative to the full set of 20 203 ab initio energies (the fitting procedure used a reduced weight for high energies, yielding a weighted rms error of 1.42 millihartree, i.e., 0.89 kcal/mole). These rms errors are comparable to the estimated error in the ab initio energies themselves; the conical intersection between the ground state and the first excited state is the largest source of error in the PES.

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“…Most of the quantum chemexperimentalists and to a somewhat lesser degree by quantum ical studies on H,CS have focussed on the molecular structures chemists (1 -9). Much of the work on the electronic and and vibrational frequencies of the lowest triplet state (7,8) or vibrational spectroscopies of thioformaldehyde in its ground the vertical electronic excitation energies (9). There have and lowest-lying excited states has recently been reviewed (1).…”

Section: Introductionmentioning

confidence: 99%

Features of the thioformaldehyde potential energy surfaces

Goddard¹

1985

Can. J. Chem.

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The structures of seven minima and five transition states of the S0 and T1 potential energy surfaces of thioformaldehyde have been located at the 3-21G* SCF level. Further calculations have been carried out to determine harmonic vibrational frequencies and to examine the effects of larger basis sets and of configuration interaction on energy differences. The molecular dissociation limit of H2 and CS is thermodynamically accessible at the energy of the lowest n,π* excited states and the singlet thiohydroxymethylenes lie only slightly too high. However, there are large barriers of ~85 to 90 kcal mol−1 to the molecular dissociation or to the 1,2-hydrogen shifts from thioformaldehyde to the thiohydroxymethylenes. The dissociation to H and HCS requires ~85.4 kcal mol−1 on the ground singlet and faces a barrier of several kcal mol−1 relative to products on the triplet surface. Any unimolecular photochemistry of thioformaldehyde is likely to require excitation to higher excited states than the lowest n,π* states.

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Theoretical studies of the electronic spectrum of thioformaldehyde

Cited by 33 publications

References 58 publications

Rydberg states in adamantanethione, thiofenchone, and thiocamphor

Rydberg states in adamantanethione, thiofenchone, and thiocamphor

Accurate analytic He–H2 potential energy surface from a greatly expanded set of ab initio energies

Features of the thioformaldehyde potential energy surfaces

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