A high-resolution study of the OH-stretch fundamental of methanol

Abstract

The OH-stretch fundamental of CH3OH has been observed with 0.025 cm-1 resolution between 3430 and 3940 cm-1 and the resulting spectrum deconvoluted using the procedure of P. A. Jansson. Approximately 600 lines have been assigned to a total of 67 P- or R-branch series and some 30 excited state levels have been determined. Of these, 14 belong to the lowest torsional state with n = 0, 13 to N = 1 and 3 to N = 2. A nonlinear least-squares fit to these levels varying the major parameters used by Y. Y. Kwan and D. M. Dennison in their analysis of the normal state produces an rms deviation between observed and calculated levels of 0.51 cm-1. Variation of all the parameters including those of the smaller Kirtman perturbation terms produces only a slight improvement in the fit. Both analyses yield a barrier height of 411 cm-1 in the excited vibrational state as compared to the normal state value of 373 cm-1. A number of unexplained anomalies appear in the spectra including large and irregular changes in the coefficient of J2 + J for different torsion-rotation states.