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Title: 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

Abstract

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 quantummore » 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.}« less

Authors:
;  [1]; ;  [2]
  1. Department of Chemistry, Brock University, St. Catharines, Ontario, L2S3A1 (Canada)
  2. Knight Chemical Laboratory, University of Akron, Akron, Ohio 44325-3601 (United States)
Publication Date:
OSTI Identifier:
698861
Resource Type:
Journal Article
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 111; Journal Issue: 11; Other Information: PBD: Sep 1999
Country of Publication:
United States
Language:
English
Subject:
66 PHYSICS; ORGANIC COMPOUNDS; FLUORESCENCE; VIBRATIONAL STATES; PHOSGENE; ELECTRONIC STRUCTURE; VISIBLE SPECTRA; ABSORPTION SPECTRA; LIFETIME; EXCITED STATES; FRANCK-CONDON PRINCIPLE; PHOSPHORESCENCE; CONFORMATIONAL CHANGES; SULFUR COMPOUNDS

Citation Formats

Moule, D.C., Burling, I.R., Liu, H., and Lim, E.C. 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. United States: N. p., 1999. Web. doi:10.1063/1.479760.
Moule, D.C., Burling, I.R., Liu, H., & Lim, E.C. 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. United States. doi:10.1063/1.479760.
Moule, D.C., Burling, I.R., Liu, H., and Lim, E.C. Wed . "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". United States. doi:10.1063/1.479760.
@article{osti_698861,
title = {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},
author = {Moule, D.C. and Burling, I.R. and Liu, H. and Lim, E.C.},
abstractNote = {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.}},
doi = {10.1063/1.479760},
journal = {Journal of Chemical Physics},
number = 11,
volume = 111,
place = {United States},
year = {1999},
month = {9}
}