We report 24 new laser lines from 13CH3OH methanol when pumped by a cw-CO2 laser. The majority of the lines are pumped by the 10R and 10SR bands of the CO2 laser. Two are pumped by the 9HP hot-band CO2 line. We measured 21 laser frequencies in this molecule; 18 from new lines and three from previously reported lines. We also remeasured and corrected the frequency of the 9P(44) pumped line as 3 378 404.87 MHz. Assignment of two lines: 10SR(17) - 77.5758 cm-1 and 10R(50) - 119.3020 cm-1, and predictions for other potential FIR laser lines with these two pumps are also included in this work.
Methanol has a rich torsion-vibration-rotation spectrum extending from the millimeter and submillimeter regions all the way through the far-infrared (FIR) and up to the near IR. High- resolution studies of the lower vibrational modes have revealed numerous perturbations arising from Fermi, Coriolis, and asymmetry resonances. A remarkable number of the perturbed energy level systems contribute to the extensive FIR laser emission observed from methanol isotopomers optically pumped by CO2 lasers. FIR laser lines involving perturbed IR levels have been invaluable aids in assigning the FIR and IR spectra and thereby locating the specific energy channels through which the CO-stretching, CH3-rocking and OH-bending vibrational modes interact with eachother, frequently via torsion-mediated coupling.
Methanol and its isotopic species have been systematically investigated as sources of far- infrared (FIR) laser emission utilizing a newly designed optically pumped FIR laser system. The system combines several different FIR laser cavity designs with the extended line coverage available from a recently developed high-resolution CO2 laser of high efficiency. New FIR laser lines have been observed pumped by fundamental band CO2 lines of high J, sequence band lines, and hot-band CO2 transitions. The new FIR laser lines extend over a broad spectral region, and contribute significantly to the frequency coverage of the optically pumped FIR laser. Many new short-wavelength lines have been observed for normal CH3OH using a 2-m-long Fabry-Perot FIR laser cavity. Accurate heterodyne measurements have been made of the FIR laser frequencies and the CO2 laser pump offsets for many of the new lines.
A weak infrared band above the strong C-0 stretching band in CH3I8OH is identified as the in-plane CH3-rocking mode. Numerous P, Q and R branches have been assigned in the high-resolution FTIR spectrum. The energy level pattern in the excited state shows that the torsional barrier height increases markedly by in going from the ground to the excited state. The band overlaps well with the 9.6 μm CO2 laser band, and six CH3-rock FIR laser transition systems are identified.
High-resolution FTIR spectra of the weak CD3-rocking bands of CD3OH and 13CD30H have been obtained. These bands lie below the strong C-0 stretching bands, and show a rather different structure. Numerous P, Q and R branch series have been assigned, from which the branch origins have been determined. The structure of the bands and the separation of n=0 and n=l branch origins indicate a substantial increase of about 31% in the torsional barrier height V3 from the ground to the CD3-rock states, but the usual energy level model does not appear to reproduce the observed branch origin patterns.