Symmetry segregation of the vibronic levels within the S1<--S0 system of thiophosgene, Cl2CS, by optical-optical double resonance spectroscopy

The first singlet-singlet electronic system, S1<--S0, in thiophosgene has been recorded as a laser induced fluorescence (LIF) excitation and an optical-optical double resonance (OODR) spectrum under jet-cooled conditions. In the OODR process, the sum of the frequencies of the pump and probe lasers must be fixed to the energy difference between a pair of vibronic levels in the S2(v') and S0(v") states. Detection is through the fluorescence from the S2 state. The blocking of a spectrum into its four possible symmetry components is obtained by adjusting the total pump+probe energy such that it matches the energy difference between symmetry selected levels in the S2 and S0 electronic states. In this method the pump laser is used to excite a group of "hot" sequence bands that involve combinations of the nu4 and nu6 antisymmetric vibrations. The additional data that were collected by this method were used to update and refine the analyses of the spectrum. Magnetic dipole transitions are reported for the first time.