EVALUATION OF AM1-CALCULATED RADICAL-CATION ION-NEUTRAL COMPLEXES

AM1 semiempirical molecular orbital calculations are reported for 20 i on-neutral complexes, including hydrogen-bonded complexes, presumably involved in the gas-phase unimolecular decomposition of simple organic radical cations. The systems investigated are [C2H4O2].+, [C2H5NO].+, [C2H6O].+, [C2H6O2].+, [C3H6O2].+, [C3H6O2].+, [C3H8O].+, and [C3H8O2 ].+. The AM1 results are compared with ab initio molecular orbital cal culations at different levels of theory up to MP3/6-31G(d, p)//SCF/6-3 1G(d) + ZPVE and the available experimental data. AM1 fails to predict some local minima and the equilibrium geometries calculated for sever al complexes are found to be qualitatively different from those predic ted by the ab initio calculations. However, reasonable agreement is ge nerally found for the stabilization energies of the complexes toward d issociation into their loosely bound components. (C) 1993 by John Wile y & Sons. Inc.