MOLECULAR DECOMPOSITIONS OF ACETALDEHYDE AND FORMAMIDE - THEORETICAL-STUDIES USING HARTREE-FOCK, MOLLER-PLESSET AND DENSITY-FUNCTIONAL THEORIES

Optimized geometries and vibrational frequencies for all reactants, tr ansition states and products of the unimolecular decompositions of ace taldehyde (CH3CHO) to CO + CH4 and to H-2 + CH2CO, and of formamide (N H2CHO) to CO + NH3 and to H-2 + HNCO were investigated at the HF, MP2 and B3LYP levels of theory with the 6-31G(d,p) basis set. Total energi es for all species were calculated with the 6-311G(d,p) basis set at t he MP4 level at both the HF and MP2 optimized geometries, with B3LYP a t the B3LYP optimized geometries, and with Gaussian-2 theory. The effe cts of basis sets and correlation corrections on barrier heights, reac tion enthalpies, and molecular structures are discussed. Most notable are the similarities in barrier heights for any level of theory which incorporates electron correlation. Inclusion of electron correlation h as significant effects on energetics, and for some geometrical paramet ers, including a change in point group symmetry for the transition sta te in the decomposition of NH2CHO to CO + NH3. Very good agreement wit h experiment, both for structures and energetics, is given by B3LYP th eory.