An optical-optical double resonance probe of the lowest triplet state of jet-cooled thiophosgene: Rovibronic structures and electronic relaxation

摘要

The vibrational structure, rotational structure, and electronic relaxation of the "dark" T-1 (3)A(2)(n,pi(*)) state of jet-cooled thiophosgene have been investigated by two-color S-2 <- T-1 <- S-0 optical-optical double resonance (OODR) spectroscopy, which monitors the S-2 -> S-0 fluorescence generated by S-2 <- T-1 excitation. This method is capable of isolating the T-1 vibrational structure into a(1), b(1), and b(2) symmetry blocks. The fluorescence-detected vibrational structure of the T-z spin state of T-1 shows that the CS stretching frequency as well as the barrier height for pyramidal deformation are significantly greater in the (3)A(2)(n,pi(*)) state than in the corresponding (1)A(2)(n,pi(*)) state. The differing vibrational parameters of the T-1 thiophosgene relative to the S-1 thiophosgene can be attributed to the motions of unpaired electrons that are better correlated when they are in the excited singlet state than when they are in the triplet state of same electron configuration. A set of T-1 structural parameters and the information concerning the T-1 spin states have been obtained from least-square fittings of the rotationally resolved T-1 <- S-0 excitation spectrum. The nearly degenerate vertical bar x > and vertical bar y > spin states are well removed from vertical bar z > spin component, indicating that T-1 thiophosgene is a good example of case (ab) coupling. The decay of the vertical bar z > spin state of T-1 thiophosgene, obtained from time-resolved S-2 <- T-1 <- S-0 OODR experiment, is characteristic of strong-coupling intermediate-case decay in which an initial rapid decay is followed by recurrences and/or a long-lived quasiexponential decay. (c) 2006 American Institute of Physics.