C2N2photodissociation at 1576 Aring;. I. CN(Athinsp;2Pgr;) radiative lifetimes, nascent vibrational distribution, and C2N2quenching

摘要

Photodissociation of C2N2at the 1576 Aring; F2laser line generates CN(Athinsp;2Pgr;) up to the thermodynamic limit ofv=5, with a bimodal vibrational distribution peaking atv=0 andv=2. Radiative lifetimes for the six observed levels have been obtained by extrapolating time decays to zero pressure, and the data show rapidly decreasing lifetimes with increasingv, in accord with recent theoretical predictions, and contrary to previous experimental determinations. The range of lifetimes observed is 4.3ndash;8.5 mgr;s. Quenching of these levels by the parent molecule shows a factor of 12 increase in rate coefficient in going fromv=0 tov=5, correlated to the energy gap between theAthinsp;2Pgr; state and the closest lowerXthinsp;2Sgr;+level, suggesting that the quenching mechanism is one involving cross relaxation between CN(A) and CN(X).