Ab initio electron affinities of AlH, SiH, GaH, and GeH, including characterization of bound excited states of SiH− and GeH−

Ab initio benchmark calculations are reported for the diatomic hydrides of Al, Si, Ga, and Ge and their negative ions using correlation consistent basis sets and several correlated methods. Adiabatic electron affinities for the 0–0 transition were found to be 0.193, 1.256, 0.131, and 1.251 eV for AlH, SiH, GaH, and GeH, respectively, at the RCCSD(T)/aug-cc-pVQZ level of theory. Excitation energies (T0) of the a1Δ and b1Σ+ bound excited states were found to be 0.560 and 1.017 eV for SiH− and 0.595 and 1.026 eV for GeH− at the MRCI + Q/aug-cc-pVQZ level. Selected spectroscopic constants are reported for the eight negative ion states.