OBSERVATION OF 3-LEVEL AND COLLISIONALLY INDUCED 4-LEVEL INFRARED-INFRARED DOUBLE-RESONANCE EFFECTS IN (CH3F)-C-12

A series of three-level and collisionally induced four-level infrared-infrared double resonance effects have been recorded and analyzed for 12CH3F. In each case a transition in the nu-3 band was pumped by a fixed-frequency near-resonant CO2 laser while a transition in either the fundamental nu-3 band or the 2-nu-3 <-- nu-3 band was probed by a continuously tunable infrared-microwave sideband laser. The recorded line shapes were analyzed either by the usual three-level double-resonance equations or by a four-level line shape equation based on a sum of Keilson-Storer collision kernels. The DELTA-k = 3n selection rule for collisionally induced rotational transitions has been confirmed and the four-level double resonances for DELTA-k = 0 show sharp transferred spikes. In addition, all the four-level double resonances include a Gaussian contribution attributed to V-V energy transfer that does not follow apparent selection rules. The widths of the spikes increase as the absolute value of the difference in the J values of the pump and probe increases. The line shapes of the spikes have been used to estimate values of the root mean square change in velocity upon collision.