Spectroscopic properties and spin–orbit coupling of electronic excited states of the germanium dimer

The electronic structure and spectroscopic properties of the germanium dimer have been investigated by high-level ab initio calculations with consideration of spin–orbit coupling (SOC). The potential energy curves (PECs) of 19 Λ–S states, as well as those of 52 Ω states generated from the Λ–S states, are calculated by the multireference configuration interaction plus Davidson correction (MRCI + Q) method. The properties of the F3Σ+u1−X3Σ−g1 and H3Σ−u1−X3Σ−g1 transitions as well as the interactions of the F3Σ+u and H3Σ−u states with other excited states induced by SOC are investigated based on the calculated SO matrix and the PECs of the Ω states. Our results indicate that the previously observed spectra of Ge2 in the range 20 500–22 000 cm−1 should be assigned as the transition between the Ω = 1g component of the X3Σ−g state and Ω = 1u of the F3Σ+u state. Moreover, owing to the strong SOC with the repulsive 25Πu state, the H3Σ−u state is predissociative, leading to the Ge(3P2) + Ge(3P1) channel at vibrational levels higher than v′ = 6. Our theoretical study would provide comprehensive information and shed light on understanding the spectroscopy and dynamics of the electronic excited states of Ge2.