ABINITIO MOLECULAR-ORBITAL CALCULATIONS ON THE PROTONATION OF ACETONE MONOMER AND DIMER

Ab initio molecular-orbital calculations have been carried out on acetone (Ac), some protonated acetone clusters (H+Ac and H+Ac2), and their isomers to compute minimum-energy geometries and harmonic vibrational frequencies. Standard reaction enthalpies (DELTA-H(THETA)) have also been computed for the reactions Acn-1H+ + Ac = AcnH+; n = 1, 2 and compared with available experimental values. A number of basis sets have been employed in the calculations, which were performed at both the Hartree-Fock and MP2 levels to investigate the effects of basis-set size and electron correlation on the computed structures and relative energies of these protonated clusters. Correction for BSSE, by the full counterpoise method, was found to be important at the MP2 level. A hitherto untried basis set, denoted as Y, was found to give results of comparable quality to those of large and more complete basis sets. From the results obtained, a number of conclusions are drawn on the possibility of extending these calculations to larger cluster sizes.