State-Resolved Study of Collisional Energy Transfer between A 2 Pi v=7 and X 2 Sigma(+) v=11 Rotational Levels of CN

摘要

Collisional transfer from the A 2Pi state of Cylandide N has been studied with initial and final state resolution by an optical optical double resonance technique. Specific rotational levels in the V = 7 vibrational manifold of the A state of CN in a flow of several Torr of argon are prepared by pulsed laser excitation in the A -X (7, 2) band. After a short time delay, a second laser probes the populations of quantum levels in this vibrational manifold and in the nearly isoenergetic v = 11 manifold of the X state by fluorescence excitation in the overlapped B - A (8,7) and B - X (8, 11) bands. The interelectronic A to X transfer rate is found to be comparable to that for purely rotational collisional transitions within the A state for all incident levels studied, regardless of whether or not they possess significant X state character, because of isolated molecule non Born Oppenheimer mixing. Reflecting the near homonuclear character of the CN-Ar interaction potentials, the final X state populations exhibited a significant even-odd alternation as a function of the final rotational angular momentum quantum number. These populations could be adequately fit by the sudden scaling relationship for Pi to Sigma cross sections. (Reprints).