THE (X)OVER-TILDE ALOH-(X)OVER-TILDE HALO ISOMERIZATION POTENTIAL-ENERGY HYPERSURFACE

Ab initio molecular electronic structure theory has been used to study the AlOH-HAlO unimolecular isomerization reaction on the singlet ground state potential energy surface. Electron correlation effects were included via configuration interaction and coupled-cluster methods. Basis sets as complete as triple zeta plus two sets of polarization functions and a set of higher angular momentum functions [TZ(2df,2pd)] were employed. The classical barrier for hydrogen migration from X HAlO to X AlOH is predicted to be 38.4 kcal mol-1 using the TZ(2df,2pd) basis set with the coupled-cluster method including all single and double excitations with the effect of connected triple excitations included perturbatively [CCSD(T)]. After correction for zero-point vibrational energies (ZPVEs), an activation energy of 3 6.6 kcal mol-1 is obtained. The DELTAE for isomerization is -42.2 ( -40.5 with ZPVE correction) kcal mol-1 at the same level of theory. The dipole moments of HAlO and AlOH in their equilibrium geometries are 4.525 and 1.040 Debye, respectively, at the same level of theory. A comparison is also made between a theoretically predicted harmonic vibrational frequency and a recently determined experimental fundamental frequency for X AlOH.