Knowledge Bank

The lineshapes of transferred spikes in the velocity distribution observed by infrared-infrared four-level double resonance have been analyzed by using a Keilson-Storer type collision $kernel.2$ The transitions have been observed by pumping a fundamental transition that is in near coincidence with a $CO2$ laser and probing a hot-band transition by means of an infrared microwave sideband laser spectrometer. Detailed analyses have been performed for the lineshapes of the double resonance effects in the saR(1,0) and saQ(3,3) transitions in the $2\nu 2\cdot \nu 2$ hot band under the influence of pumping of the asR(2,0) transition in the $\nu 2$ band. Each lineshape consists of a Gaussian part centered on the resonance frequency of the probed transition and a transferred spike offset from the resonance frequency by the difference between the frequency of the pump laser and the resonance frequency of the pumped transition. The Gaussian part is subtracted from the experimental lineshape and the difference is fit to a sum of two Keilson-Storer lineshapes. We tentatively interpret the two contributions to the transferred spike to be the result of $\Delta J=\pm 1$ and $\Delta J=\pm 2$ collisionally-induced transitions. The transferred spike observed for the saR(1,0) transition ($\Delta K=0$ collisions) is much sharper than that observed for the saO(3,3) transition ($\Delta K=3$ collisions). The pressure dependence of the observed double resonances will also be discussed.