Rotationally Resolved Intramolecular Processes in Benzene

The influence of the molecular rotation on intramolecular processes is investigated for both a non‐reactive and a reactive large polyatomic system. The non‐reactive system chosen is the S 1 state of benzene, C 6 H 6 . Doppler‐frec spectra of the 14 0 1 band show isolated rotational perturbations due to a highly selective coupling of the “light” zero‐order states to “dark” rovibrational states within the S 1 state. These perturbations are caused by J, K dependent Coriolis coupling, which will induce energy randomization in the excited molecule. The reactive process investigated is the unimolecular dissociation of rotationally selected excited benzene cations. It is found that energy is completely randomized and the benzene cations behave like a statistical system. Dissociation rates are found to decrease with rotational quantum number, J . It is concluded that rotational selection has to be included in precise experiments and theoretical models of intramolecular processes.