Saturation transfer studies on doorway states for CH$_{2}$ intersystem crossing

Double-resonance transient photobleaching kinetics of singlet and mixed singlet-triplet eigenstates of CH$_{2}$ to characterize the closely related processes of rotational energy transfer and collision induced intersystem crossing in methylene will be reported. Qualitative features of the state-to-state rotational energy transfer matrix are revealed. Selective bleaching of individual eigenstates of mixed state (doorway) pairs shows very efficient collisional interconversion within the mixed-state pair.