Additions and Corrections - Structure and Tunneling Dynamics of Malonaldehyde. A Theoretical Study.

The geometry and harmonic vibrational frequencies of equilibrium malonaldehyde and of the transition state for the symmetric intramolecular hydrogen atom transfer have been determined at the SCF level of theory (using a slightly better than double-basis set). All geometrical parameters were fully and simultaneously optimized by using SCF gradient techniques. Comparison of the equilibrium structure with the structure determined from microwave spectra shows good agreement in most respects, although there are a few differences. At the C/sub s/ equilibrium geometry and the C/sub 2//sub v/ transition state large scale configuration interaction (all single and double excitations) calculations were carried out to determine the barrier height for the symmetric hydrogen atom transfer; including a correction for quadruple excitations, this gives a classical or ''bare'' barrier height of 8.0 kca./mol. A one-dimensional model for the tunneling dynamics of H-atom transfer leads to a tunneling splitting in the ground vibrational state of approx. 18 cm/sup -1/, in relatively good agreement with the experimental value. It is noted, though, that the value of the splitting is sensitive to the potential surface parameters (i.e., bare height, frequencies) and that there is also uncertainty about the accuracy of the one-dimensional description of the tunneling.