The cavity ringdown spectrum of the visible electronic system of thiophosgene: An estimation of the lifetime of the T[sub 1]([tilde a]; [sup 3]A[sub 2]) triplet state

Journal Article · Wed Sep 01 00:00:00 EDT 1999 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.479760· OSTI ID:5903302

Moule, D C; Burling, I R ^[1]; Liu, H; Lim, E C ^[2]

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1. Department of Chemistry, Brock University, St. Catharines, Ontario, L2S3A1 (Canada)
2. Knight Chemical Laboratory, University of Akron, Akron, Ohio 44325-3601 (United States)

To obtain insights into the photophysical properties of collision-free T[sub 1]([tilde a] hthinsp;[sup 3]A[sub 2]) thiophosgene, Cl[sub 2]CS, the cavity ringdown (CRD) spectrum of the T[sub 1][l arrow]S[sub 0] absorption system was recorded under supersonic jet conditions and compared with the corresponding excitation spectrum of the total emission. It was found that none of the T[sub 1][l arrow]S[sub 0] bands in the CRD spectrum appears in the excitation spectrum, indicating that the T[sub 1] thiophosgene decays almost exclusively by the nonradiative T[sub 1][r arrow]S[sub 0] intersystem crossing (ISC). An estimation of the T[sub 1] nonradiative lifetime was made using the T[sub 1][endash]S[sub 0] spin-orbit coupling and the Franck[endash]Condon factors for the T[sub 1][r arrow]S[sub 0] ISC based on the [ital ab initio] equilibrium structures and vibrational frequencies for the T[sub 1] and S[sub 0] states, computed at the MP2/6-31G(d,p) and MP4/6-31G(d,p) level of theory. The nonradiative life, calculated as the 1/e of the survival probability, is approximately 20 ps for barrier heights of 770[endash]845 cm[sup [minus]1] and out-of-plane angles of 32.07[degree][endash]32.69[degree]. (The thiophosgene adopts a pyramidal conformation with the C[double bond]S bond bent from the ClCCl plane by about 32[degree].) The computed lifetime is comparable to the lower-limit lifetime of [approximately]50 ps obtained from the quantum yields [Phi][sub P][le]10[sup [minus]3][Phi][sub F] with [Phi][sub F][approx]1.0 and the measured S[sub 1] fluorescence lifetime of 4 [mu]s. The short T[sub 1] nonradiative lifetime of thiophosgene can be attributed to the large matrix elements of the T[sub 1][endash]S[sub 0] spin-orbit coupling (V=150 hthinsp;cm[sup [minus]1]) and the strong out-of-plane deformation of the T[sub 1] state relative to the planar S[sub 0] state, that provides the large Franck[endash]Condon factors for the T[sub 1][r arrow]S[sub 0] ISC. It is proposed that a similar pyramidal deformation is also responsible for the absence of phosphorescence from T[sub 1] thiocyclobutanone. Consistent with this supposition, T[sub 1] cyclopentanone, which is nearly planar at the thiocarbonyl carbon center, exhibits strong phosphorescence under similar experimental conditions. [copyright] [ital 1999 American Institute of Physics.]

• OSTI ID: 5903302
• Journal Information: Journal of Chemical Physics, Vol. 111:11; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
ABSORPTION SPECTRA
CONFORMATIONAL CHANGES
ELECTRONIC STRUCTURE
EXCITED STATES
FLUORESCENCE
FRANCK-CONDON PRINCIPLE
LIFETIME
ORGANIC COMPOUNDS
PHOSGENE
PHOSPHORESCENCE
SULFUR COMPOUNDS
VIBRATIONAL STATES
VISIBLE SPECTRA
CARBONIC ACID DERIVATIVES
ENERGY LEVELS
LUMINESCENCE
ORGANIC CHLORINE COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
SPECTRA
664200* - Spectra of Atoms & Molecules & their Interactions with Photons- (1992-)