Optical spectroscopy of the previously unobserved palladium monosulfide (PdS) radical

The optical spectra of the palladium monosulfide (PdS) molecule in gas phase have been investigated for the first time through laser-induced fluorescence (LIF) and single-vibronic-level (SVL) emission spectroscopies. The I3Σ- - X3Σ- transition system containing 16 vibronic bands was identified in the LIF spectra, covering the energy range of 22 030-23 400 cm-1. The spectra with rotational resolution allowed for the determination of the molecular constants in both the ground X and excited I electronic states, involving the spin-orbit splitting, rotational constant, vibrational frequency, and isotope shift. Isotopically resolved SVL emission spectra permitted the observation of the spin-orbit splitting, vibrational frequency, and vibrational isotope shift of the X3Σ-0+,1 and A3Π2,1,0-,0+ states as they transitioned from the excited I state to the vibrational levels of the X and A states. Ab initio calculations presented plenty of the Λ-S and Ω states of PdS below 28 000 cm-1 and provided strong support for the assignments of the experimental observation.