A FULL-DIMENSIONAL SEMICLASSICAL CALCULATION OF VIBRATIONAL-MODE SELECTIVITY IN THE TUNNELING SPLITTING IN A PLANAR MODEL OF MALONALDEHYDE

A semiclassical method is used to treat proton tunneling in a planar m odel of malonaldehyde. Classical trajectories were calculated on a rea listic potential-energy surface and WKB tunneling probabilities were c alculated at turning points on the barrier separating the two equivale nt potential wells. The calculated ground-state splitting, 24.5 cm-1, is in good agreement with the experimental value of 21.6 cm-1. Vibrati onal mode selectivity was studied by calculating the splitting for all 15 modes for 2 kcal/mol excitation energy (35 kcal/mol total energy). The results show significant mode specific effects for all except som e C-H stretching modes. This study demonstrates that multidimensional semiclassical tunneling can be readily and accurately treated.