FTIR spectroscopy and FIR laser assignments for 13CD3OH

Abstract

The various isotopic species of methyl alcohol have proved in recent years to be fertile sources of optically-pumped far-infrared (FIR) laser lines. The relatively exotic 13CD3OH form, in particular, turned out to produce the second most efficient FIR line known,1 creating considerable spectroscopic interest. We have examined spectra of this molecule previously ,2-4 and determined some of the molecular constants for the ground, C-O stretch and CD3-rock vibrational states, as well as possible assignments for a few IR-pump/FIR-laser transition systems. Spectroscopic and FIR laser studies have also been carried out by Pereira and co-workers,5,6 and many additional FIR laser lines have been found. Because several of the known FIR lines are pumped by CO2 laser lines of the 9R branch lying above the C-O stretch band, we have extended our spectroscopic investigations into the higher IR regions to identify new vibrational bands which might account for the FIR laser emission. Further motivation came from the apparent large increase in torsional barrier height found for the CD3-rock state, which prompted our curiosity about the barrier heights for other vibrational modes. In this paper, we discuss our progress to date in the study of new IR spectral regions of 13CD3OH, and the determination of molecular constants and FIR laser assignments.