Lifetime measurements of selectively excited rovibrational levels of the V ¹B₂ state of CS₂

The radiative lifetimes of selectively excited rovibrational levels of the V 1B2 state of the CS2 molecule have been measured under collision-free conditions in a cold molecular beam using a pulse-modulated frequency-doubled single-mode cw dye laser. Pure exponential fluorescence decays were found for all excited levels. The lifetimes, scattering considerably in the range of 2–13 μs, give evidence of interactions of the V 1B2 state with background states. A deperturbation analysis performed for rotational levels involved in local two-level interactions yields detailed quantitative information on the V 1B2 state and on the background levels. It is shown that these levels represent rovibrational levels of the B2(3A2) state and highly excited rovibrational levels of the X 1Σg+ electronic ground state. The coupling mechanisms are: (1) the spin–orbit interaction between the V 1B2 state and the B2(3A2) state where the latter is coupled to the X 1Σg+ ground state by spin–orbit/vibronic and spin–orbit/Coriolis interaction and (2) the Coriolis coupling of the V 1B2 state to the X 1Σg+ ground state. Further sources of perturbations are the spin-uncoupling in the 3A2 state and the Renner–Teller coupling of the V 1B2 state to the 1A2 state. From the measured radiative lifetimes of the background states information on the electronic structure of the CS2 molecule is gained.