Characterization of the X2A1, A2B1, and X2Pi electronic states of the Ga2H molecule and the X2A' and A 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 (2)Pi) and H-bridged (X (2)A(1) and A (2)B(1)) Ga(2)H isomers and two isomerization transition states (X (2)A(') and A (2)A(")) connecting the three minima. Dipole moments and vibrational frequencies are also obtained. The global minimum X (2)A(1) 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 A (2)B(1) state. The X (2)A(1) state lies 5.4 kcal mol(-1) below the X (2)Pi 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 (2)A(') and A (2)A(") transition states are determined to be 3.3 and 5.3 kcal mol(-1), respectively. The reverse isomerization barrier between the X (2)A(1) GaHGa structure and the X (2)Pi 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.