State-resolved thermalization of singlet and mixed singlet-triplet states of CH_2

摘要

The role of mixed states in the collision-induced thermalization,intersystem crossing,and reactive loss of CH_2(alphaA_1)has been monitored using Doppler-resolved transient frequency modulation absorption spectroscopy.Singlet CH_2 is produced in a hot initial distribution of translation and rotational energy states in the 308 nm photodissociation of ketene in a large excess of argon.Collisions with Ar and ketene cool the translational and rotational degrees of freedom,while depleting the total singlet CH_2 population through reaction and intersystem crossing.Direct monitoring of the time-dependent populations of rotational levels containing mixed singlet and triplet character reveals a rapid interconversion between the two components,but no discernable difference between the kinetics of the pure singlet and mixed states at longer times.