AB-INITIO STUDY OF STRUCTURE AND REACTIVITY OF H2CO.H2O-CENTER-DOT+ AND RELATED RADICAL CATIONS

An ab initio Hartree-Fock and Moller-Plesset study of the radical cati ons obtained by ionization of the formaldehyde-water hydrogen bonded d imer is reported. Two radical-cation complexes with different bonding patterns were identified at the SCF level (2a and 2b), one of which (2 a) closely resembles the formaldehyde radical cation (FRC) solvated by a water molecule. Geometry optimization at the MP2 level, however, de monstrates that 2a is not stable as a FRC-water complex. It undergoes proton transfer instead, to end up as a H3O+.HCO. complex, with the hy dronium ion bound to the C atom of the radical. The reaction paths for this complex were investigated and compared with those of FRC. It was found that the most stable complex on these reaction paths is obtaine d after a H3O+ 1,2-shift in the FRC. This product, best described as a complex of HCO. and H3O+, is analogous to the recently reported HO... .H3O+ and HCO....NH4+ and lies in a well deep enough to be observable experimentally. Different possible outcomes of the experiments are dis cussed in the light of the relative stability of the complexes obtaine d on the reaction paths.