Laser-Excited Electronic Fluorescence: Collision-Induced Radiationless Transitions in Propynal

Abstract

A pulsed dye laser tuned to 3821 Å is used to excite vapor phase propynal molecules, making possible the observation of time resolved luminescence from the A″ states. The collision‐free lifetime for the ground vibrational level of the ¹A″ electronic state is 0.978 μsec. Quenching of this state by 19 different collision partners with dipole moments ranging from 0 to 3.95 D has been examined at room temperature. Cross sections ranging from 8 to 175 Ų have been found. The larger cross sections appear to be associated with the more polar collision partners and evidently arise from long range forces. Evidence is presented that quenching is the result of a spin‐allowed transition. A somewhat general theory for collision‐induced radiationless transitions is proposed which appears to correlate the observations for propynal. As an example of the applicability of this model to other molecular systems, the theory is applied to earlier data on I₂.