The ground and low-lying electronic states of OsO

Abstract

The significant electron correlation and relativistic effect in the 5d transition atoms lead to a complex electronic structure of their compounds. Even for the osmium monoxide (OsO) molecule, the ground electronic state has been posing a considerable challenge for both theoretical and experimental investigations so far. Here, we report the observation and identification of the electronic states of OsO in low energy through laser-induced fluorescence and dispersed fluorescence spectra. There are six excitation bands rotationally resolved in the energy range of 15 000–23 100 cm−1, thus enabling the determination of the ground X3Π2 state and the rotational constants in the upper and lower states. The spin–orbit splitting and vibrational frequency of the ground state and three low-lying Ω states are obtained from the emission spectra. In addition, by performing high-level ab initio calculations, we obtained detailed spectroscopic properties for numerous Λ-S and Ω electronic states below 25 000 cm−1, which support the spectral assignments derived from experimental measurements. The results provide quantitative evidence for the significant relativistic effect on the bonding of OsO, as well as a foundation for describing its electronic structure.