Infrared-infrared double resonance of methyl fluoride in foreign gases

Abstract

Infrared-infrared double-resonance spectra have been recorded for samples of methyl fluoride gas in an excess of hydrogen, helium, argon, and xenon, as well as for mixtures of 12CH 3F and 13CH 3F. The double-resonance effects appear as a narrow transferred spike superimposed on a broad Gaussian lineshape of the expected Doppler width. When the foreign gas has a dipole moment or is a relatively light perturber, the spike dominates the lineshape, but when the foreign gas is a relatively heavy atom, the Gaussian dominates. The spectra for all of the samples show evidence of a Δ k = 3 n ( n = an integer or zero) selection rule for collisionally induced rotational transitions. The spectra with argon and xenon as foreign gas demonstrate that collisions with these atoms can induce direct vibration-rotation energy changes from v 3 = 1 to v 6 = 1 in methyl fluoride and that the selection rule for these transitions is Δ( k − l) = 3 n. The double-resonance spectra with argon and xenon as a foreign gas also show a frequency shift that is substantially larger than the shift for single-resonance spectra in the same mixture. One-dimensional collision kernels have been calculated by classical mechanics and appear to display most of the characteristics of the experimental spectra.