STRUCTURE AND VIBRATIONAL-SPECTRA OF METHANOL CLUSTERS FROM A NEW POTENTIAL MODEL

The structures and vibrational spectra of small methanol clusters from dimer to decamer have been calculated using a newly developed intermo lecular potential which is essentially based on monomer wave functions . Special care has been taken for the description of the electrostatic interaction using a distributed multipole representation and includin g a penetration term. In addition, the potential model consists of rep ulsion, dispersion, and induction terms. Based on this potential model cluster structures have been calculated. The lowest energy dimer conf iguration is linear, while from trimer to decamer for the most stable structures ring configurations were found. Tetramer, hexamer, and octa mer have S4-, S6-, and S(8-)symmetry, respectively. Vibrational spectr a of the CO stretch and the OH stretch mode have been determined in th e harmonic and in the anharmonic approximation using perturbation theo ry and variational calculations. Up to the tetramer the experimental s pectra of the CO stretch mode are well reproduced, for larger clusters an increasing blueshift with respect to the experimental evidence is found. The experimental data for the OH stretch mode of the dimer are fairly well reproduced in all approximations, however, the spectrum of the trimer can only be reproduced using the variational calculation w hich includes Darling-Dennison resonance terms. (C) 1998 American Inst itute of Physics.