PNNL

Abstract

High-resolution Fourier Transform Spectra of CH3OH have been investigated in the infrared region from 930 -1450 cm-1 in order to map the torsion-rotation energy manifolds associated with the v7 in-plane CH3 rock, the v11 out-of-plane CH3 rock, and the v6 OH bend. Upper-state term values have been determined from the assigned spectral subbands, and have been fitted to power-series expansions to obtain substate origins and effective B-values for the three modes. The substate origins have been grouped into related families according to systemic trends observed in the torsion-vibration energy map, but there are substantial differences from the traditional torsional patterns. There appears to be significant torsion-mediated spectral fractionation, and a variety of subbands of mixed torsion-vibration parentage have been observed. For example, coupling of the v6=1 OH bend to nearby torsionally excited (v1, vt) = (1,1) CH3-rock and (v8, vt) = (1,1) CO-stretch states introduces (v6, vt) = (1,0) ? (0,1) "forbidden" subbands into the spectrum and makes the v7+v12-v12 torsional hot band stronger than the v7 fundamental. The results suggest a picture of strong coupling the OH-bending, CH3-rocking and CO-stretching modes that modifies the traditional energy structure and raises interesting and provocative questions about the torsion-vibration identity of a number of the observed states.