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3 BAND OF METHYL FLUORIDE IN SOLID PARAHYDROGEN USING A QUANTUM CASCADE LASER.
A. R. W. MCKELLAR, Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, ON K1A 0R6, Canada; ASAO MIZOGUCHI AND HIDETO KANAMORI, Department of Physics, Tokyo Institute of Technology, Ohokayama 2-12-1, Meguro-ku, Tokyo, 152-8551 Japan.
The
3 band of CH3F isolated in solid para-H2 exhibits a clearly resolved series of lines due to clusters of CH3F with residual ortho-H2 molecules, CH3F-(ortho-H2)N, with N = 0
12. We have examined this spectrum in detail using a quantum cascade laser source. Solid hydrogen crystals were formed by direct vapor phase deposition on a BaF2 window at 2 K followed by annealing (4.6 K for 10 minutes) or ``super-annealing" (7 K for 10 seconds). The cw laser (Hamamatsu Corp.) was a room temperature DFB device with output powers up to ~30 mW and a tuning range of about 1042 - 1036 cm-1 for device temperatures of 0 - 37\circ C. This power level was easily strong enough to modify the sample by means of spectral hole-burning effects. It was therefore necessary to strongly attenuate the laser in order to record normal ``static" spectra. But we also took advantage of the power to make interesting ``dynamic" measurements in which a transition could be bleached away and forced to reappear in a new position. Line widths as narrow as ~0.0065 cm-1 were observed and line profiles were Lorentzian. The N = 0 line at 1040.19 cm-1 was resolved into two closely-spaced (
0.008 cm-1) components which we believe correspond to the K = 0 (A) and 1 (E) levels of CH3F, arising from partially free a-axis rotation in the crystal. Numerous extra satellite lines were observed around each main feature (N = 0, 1, 2, 3, 4) as well as some weak but sharp transitions almost mid-way between N = 0 and 1.