Vibrational Relaxation and Its Competition with Radiationless Transitions in the B12u State of Benzene

Abstract

Vibrational relaxation in the ${}^1{B}_{\text{2u}}$ state of benzene has been studied. The molecules were excited by the mercury 2537‐Å radiation or by electron impact in a low‐pressure discharge. All information about vibrational relaxation was obtained from the vibrational structure of the optical emission spectra as a function of the vapor pressure or the pressure of a foreign gas. A model is suggested describing the entire relaxation mechanism by transitions between three vibronic levels of the ${}^1{B}_{\text{2u}}$ state. These levels have different vibrational properties. Radiationless transitions are assumed to occur at different rates from the three levels. This model is applied to intersystem crossing and a photochemical process, both competing with vibrational relaxation in the ${}^1{B}_{\text{2u}}$ state of benzene.