Characterization of the X 2A1, à 2B1, and X 2Π electronic states of the Ga2H molecule and the X 2A′ and à 2A″ isomerization transition states connecting the three minima

A wide range of highly correlated ab initio methods has been used to predict the geometrical parameters of the linear (X 2Π) and H-bridged (X 2A1 and à 2B1) Ga2H isomers and two isomerization transition states (X 2A′ and à 2A″) connecting the three minima. Dipole moments and vibrational frequencies are also obtained. The global minimum X 2A1 ground state of the H-bridged GaHGa isomer is predicted to lie only 1.6 [1.9 with the zero-point vibrational energy (ZPVE) corrections] kcal mol-1 below the à 2B1 state. The X 2A1 state lies 5.4 kcal mol-1 below the X 2Π ground state of the linear GaGaH isomer at the coupled-cluster with single, double, and perturbative triple excitations [CCSD(T)] level of theory with the augmented correlation-consistent polarized valence quadruple-zeta (aug-cc-pVQZ) basis set. The full triples coupled-cluster method is found to alter these CCSD(T) predictions by as much as 0.3 kcal mol-1. The forward isomerization barriers from the linear ground state to the X 2A′ and à 2A″ transition states are determined to be 3.3 and 5.3 kcal mol-1, respectively. The reverse isomerization barrier between the X 2A1 GaHGa structure and the X 2Π GaGaH structure is predicted to be 8.6 (8.2 with the ZPVE corrections) kcal mol-1 at the aug-cc-pVQZ CCSD(T) level of theory. [ABSTRACT FROM AUTHOR]