List of committees

Abstract

The tetramethylammonium (TMA) complex with one water molecule has been treated ab initio using the 3–21G, 4–31G, 6–31G∗, 6–31G∗∗ and 6–31+G∗ basis sets as well as by the semiempirical AM1 and MNDO-PM3 methods. Full geometry optimization of the complex has been carried out with the 4–31G basis set, whereas with the other basis sets the tetrahedral angles of the TMA skeleton were fixed. Part of the potential surface for the water displacement between two neighbouring methyl groups was explored. The overall geometry obtained by ab initio energy minimization differs from that yielded by the semiempirical methods. The interaction energy, compensated for by the basis set superposition error, is of the order of l0 kcal mol−1 ; it was decomposed according to the method of Kitaura and Morokuma (Int. J. Quantum Chem., 10 (1976) 325). The polarization and charge transfer components are small. The results of the calculations on the complex are compared with neutron diffraction data (J. Turner, A.K. Soper and J.L. Finney, Mol. Phys., 70 (1990) 679) and Monte Carlo simulations of aqueous TMA salt solutions (W.L. Jorgensen and J. Gao, J. Phys. Chem., 90 (1986) 2174). The nature of the CH... O interaction is discussed.