Theoretical study of reactions between AlH((1)Sigma) and HF molecule

Reaction mechanisms between AIH ((1)Sigma) and HF molecule are theoreticall y investigated. Ab initio calculations demonstrate that there are two paral lel reaction channels: one is an addition reaction to give H2AlF via the th ree-membered ring transition state (TS) and the other is a dehydrogenation reaction to give AlF + H-2 via the four-membered ring TS. The addition reac tion is thermodynamically favorable and the dehydrogenation reaction is kin etically favorable. Thermodynamics and Eyring transition state theory (TST) with the Wigner correction are also used to compute the thermodynamic func tions, the equilibrium constants, A factors, and the rate constants of thes e reaction channels at 200-1000 K. From the thermodynamics and TST calculat ions, it is valuable to point out that consideration on the entropy and the rmal enthalpy is quite important in the study of chemical reactions on the basis of ab initio method. (C) 1999 John Wiley & Sons, Inc.