FOURIER-TRANSFORM SPECTRUM OF THE INPLANE CH3-ROCKING FUNDAMENTAL ANDVIBRATIONAL COUPLING IN C-13 METHANOL

The Fourier transform infrared spectrum of the in-plane CH3-rocking fu ndamental of (CH3OH)-C-13 has been investigated at 0.002 cm(-1) resolu tion. The rocking band is principally of parallel character and has a double-peaked Q branch and relatively wide spread subbands indicative of a substantial change in torsional barrier height. All A subbands fr om K=0 to 11 and all but one E subband from K=0 to 9 have been assigne d in the n=0 torsional state and fitted to J(J+1) power-series expansi ons to obtain the subband origins and excited-state energy structure. The effects of vibrational interactions between the CH3-rocking and CO -stretching modes are prominent in the spectrum, Coriolis coupling bet ween rocking (K-1) and CO-stretching K levels is observable for K grea ter than or equal to 6, and makes significant contributions to the sub band origins and effective B values. Several J-localized perturbations due to level-crossing resonances with CO-stretch states have been obs erved and characterized. Two reported strong far-infrared laser lines optically pumped by the 10R(26) CO2 laser line have been found to aris e through such a Delta K=3 level-crossing resonance. Modeling of the r ocking-state torsion-K-rotation energies yields a height of V-3(r)=469 .2(38) cm(-1) for the torsional potential barrier, a 26% increase over the ground state. The asymmetry K-doubling pattern in the excited sta te is qualitatively consistent with this barrier for K=2 to 4, but the K=5 rocking substate displays strongly enhanced splitting. (C) 1997 A merican Institute of Physics.