Vibrational analysis of the 460 nm band system of nickel dichloride produced in a free jet expansion

Using a free-jet expansion which incorporates a heated nozzle, we have recorded the laser excitation spectrum of the 460 nm band system of NiCl2 at a rotational temperature of ~40 K. 35Cl/37Cl isotope shifts were resolved which permit the assignment of progressions involving the symmetric stretching vibrational mode and identify a triplet splitting with spacings of 96 and 149 cm-1 which is believed to be due to spin–orbit coupling. Sequence bands involving the bending vibrational mode are also tentatively assigned. Only a small change in the symmetric stretching vibrational wave number is found between the electronic states involved in this transition (v'₁ =356 cm-1, v''₁ =360 cm-1). This result and the triplet splitting observed are discussed with respect to the possible electronic states involved and the assignment of this band system as either a Laporte forbidden g<->g transition involving the d orbitals on the Ni atom or an allowed u<->g charge transfer transition.