Saturation-dip measurements for the ν_8 C-O stretching band of CH_3OH with a CO_2-laser-microwave-sideband spectrometer

Abstract

Saturation-dip measurements for the ν8 C-O stretching band of CH3OH have been systematically carried out with a CO2-laser-microwave-sideband spectrometer operating on low- and high-J 9.6 μm P-branch CO2 laser lines. Frequencies of nearly 500 spectral lines, including overlapped and doublet lines unresolved in dense Doppler-limited spectra, have been measured with a resolution of 0.4MHz and absolute accuracy of the order of ±100 kHz. Over 200 frequency combination loops have been formed from the present and previous sub-Doppler observations, unambiguously confirming the infrared transition assignments, and refined term values have been determined for 623 excited vibrational levels. These results constitute a substantial database of high-accuracy frequency reference standards for CH3OH in the 10 μm region, with applications in frequency calibration, in detailed studies of the complicated methanol intermode vibrational interactions, and in the interpretation of optically pumped far-infrared laser emission.