The X̃ AlOH–X̃ HAlO isomerization potential energy hypersurface

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Abstract
Ab initio molecular electronic structure theory has been used to study the AlOH–HAlO unimolecular isomerizationreaction on the singlet ground statepotential 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 X̃ HAlO to X̃ 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 36.6 kcal mol−1 is obtained. The ΔE 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 X̃ AlOH.