HIGH RESOLUTION STUDIES OF THE \nub{3} BAND OF METHYL FLUORIDE IN SOLID PARAHYDROGEN USING A QUANTUM CASCADE LASER

Author Institution: Steacie Institute for Molecular Sciences, National Research; Council of Canada, Ottawa, ON K1A 0R6, Canada; Department of Physics, Tokyo Institute of Technology; Ohokayama 2-12-1, Meguro-ku, Tokyo, 152-8551 JapanThe \nub{3} band of CH$_3$F isolated in solid $para$-H$_2$ exhibits a clearly resolved series of lines due to clusters of CH$_3$F with residual $ortho$-H$_2$ molecules, CH$_3$F-($ortho$-H$_2$)$_N$, with $N$ = 0 $\sim$ 12. \textbf{119}, 4731 (2003).} 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 BaF$_2$ 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 $\wn$ for device temperatures of 0 - $37^irc}$ 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 $\wn$ were observed and line profiles were Lorentzian. The $N$ = 0 line at 1040.19 $\wn$ was resolved into two closely-spaced ($\sim$0.008 $\wn$) components which we believe correspond to the $K$ = 0 ($A$) and 1 ($E$) levels of CH$_3$F, arising from partially free $a$-axis rotation in the crystal. \textbf{129}, 104502 (2008).} 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