Characterization of the X̃A12, ÃB12, and X̃Π2 electronic states of the Ga2H molecule and the X̃A′2 and ÃA″2 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 (XΠ2) and H-bridged (XA12 and AB12) Ga2H isomers and two isomerization transition states (XA′2 and AA″2) connecting the three minima. Dipole moments and vibrational frequencies are also obtained. The global minimum XA12 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] kcalmol−1 below the AB12 state. The XA12 state lies 5.4kcalmol−1 below the XΠ2 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 0.3kcalmol−1. The forward isomerization barriers from the linear ground state to the XA′2 and AA″2 transition st...