Ab initio study of the structures of CH 3 NH 3 + and CH 3 PH 3 + in aqueous solution

The purpose of this work was to determine quantitatively the structures of CH 3 NH 3 + and CH 3 PH 3 + in aqueous solution. For this purpose, the structures of CH 3 NH 3 + (H 2 O) n were optimized using MP2/6–31G(d) ( n  = 0, 1, 2, 3, 4, 5, 6) and RHF/4–31G ( n  = 0, 1, 2, 3, 4, 5, 6, 9, 21) and the structures of CH 3 PH 3 + (H 2 O) n ( n  = 0, 1, 2, 3) were optimized using MP2/6–31+G(d,p). Based on these structures, the structure of CH 3 NH 3 + in aqueous solution was predicted as follows: C—N = 1.479 Å, N—H = 1.047 Å, C—H = 1.088 Å, NCH = 108.9° and CNH = 108.5°. The C—N bond length of CH 3 NH 3 + in aqueous solution is predicted to be smaller than that in the gas phase by 0.03 Å. The N—H bond lengths of CH 3 NH 3 + in aqueous solution are predicted to be longer than those in the gas phase by 0.02 Å. The structure of CH 3 PH 3 + in aqueous solution was predicted as follows: C—P = 1.808 Å, P—H = 1.394 Å, C—H = 1.087 Å, PCH = 109.5° and CPH = 109.9°. The structure of CH 3 PH 3 + in aqueous solution is predicted to be similar to that in the gas phase. Copyright © 2001 John Wiley & Sons, Ltd.