Knowledge Bank

Collision-induced transitions have been studied by microwave double resonance for the $(3\leftarrow 2)p-(2\leftarrow 1)S$ rotational level system of OCS in the first excited bending state, $V2=1$, with the individual M-substates resolved by a Stark field. The $\ell$-doubling of the levels leads to a rather complex spectrum with several novel and interesting features. The implications of these will be discussed in terms of collisional selection rules on J, M and parity. A notable feature is the observation of $\Delta M=2$ collisional transitions, which are forbidden under first-order dipolar selection rules. This indicates that higher-order collisional processes are important, as found previously for ground state OCS.