STUDY OF THE OVERTONE C-O STRETCHING BAND OF METHANOL BY MULTIPLE RESONANCE SPECTROSCOPY

Two microwave-sideband CO2 lasers have been used with a molecular-beam electric-resonance spectrometer to study the overtone C-O stretching vibration of methanol. Infrared-infrared double-resonance results have been obtained for levels involving the K=1 and 2, A symmetry, and the K=2, E2 symmetry species. In the A torsional symmetry case, radio frequency-infrared multiple resonance was used to obtain accurate asymmetry splittings for the vco=1 and 2, C-O stretching states. The asymmetry splitting constants determined for these states are in good agreement with the literature values for the first excited C-O stretching states. However, the nearly factor-of-2 change in the K=2 asymmetry splitting constant for the v co=2 level compared to the vco=0 and 1 level results suggests that this state is weakly perturbed. The overtone transition frequencies obtained in this work were combined with previous overtone Fourier-transform results in a global fit to a torsion-rotation Hamiltonian to refine the fundamental molecular constants for the second-excited C-O stretching state. The vco=2 torsional barrier height is found to be 372.227(3) or 374.984(7) cm-1 depending on data set used. In the analysis the overtone vibrational energy origin is constrained to 2054.831 13 cm -1. This barrier can be compared to the V0=0 and 1 values of 373.5421 and 392.35 cm-1, respectively. © 1995 American Institute of Physics.