New far-infrared laser lines and assignments for 13 CH 3 OH methanol

The 13CH3OH isotopomer of methanol has been reinvestigated as a source of far-infrared (FIR) laser emission by the use of the extended line coverage available from an efficient CO2 laser recently developed for optical pumping. With this system we have observed 19 new FIR laser lines, pumped by 11 different CO2 transitions, with five of the pump lines belonging to the new 9HP CO2 hot band. Accurate heterodyne frequency measurements of the FIR laser and the pump offset have been made for 16 FIR laser lines, including three previously reported in the literature. High-resolution Fourier-transform spectroscopic results for the CO-stretching and the CH3-rocking infrared fundamentals of 13CH3OH have been applied to assign the pump and lasing lines for five of the transition systems. One system has the novel feature that two different CO2 pump lines excite the same upper level, and hence two FIR laser lines of the identical frequency are observed for two different pump lines.