The <sup>13</sup>CH<sub>3</sub>OH 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 CO<sub>2</sub> laser recently developed for optical pumping. With this system we have observed 19 new FIR laser lines, pumped by 11 different CO<sub>2</sub> transitions, with five of the pump lines belonging to the new 9<i>HP</i> CO<sub>2</sub> 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 CH<sub>3</sub>-rocking infrared fundamentals of <sup>13</sup>CH<sub>3</sub>OH 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 CO<sub>2</sub> pump lines excite the same upper level, and hence two FIR laser lines of the identical frequency are observed for two different pump lines.
© 1995 Optical Society of America
Li-Hong Xu, R. M. Lees, E. C. C. Vasconcellos, L. R. Zink, K. M. Evenson, S. C. Zerbetto, and Adriana Predoi, "New far-infrared laser lines and assignments for 13CH3OH methanol," J. Opt. Soc. Am. B 12, 2352-2359 (1995)