The NbN C3Π−X3Δ (1–0) band: Experimental and theoretical study of the spin-orbit interaction between the C3Π and e1Π states

Abstract

The NbN C3Π−X3Δ (1–0) band is studied in the free-jet setup. The spin-orbit interaction between v=1 of C3Π1 and e1Π states destroyed the symmetric splitting of C3Π substates. Unusually high 685cm−1 spin-orbit interaction matrix element between them pushed the 3Π1 substate below 3Π0 component. Our ab initio calculations estimate 3Π2-3Π0 separation 414cm−1, which is in an excellent agreement with the observed value 404cm−1, and places the 3Π1 state 244cm−1 below 3Π0 state, in somewhat poor agreement with the experimental separation of 449cm−1. This error is primarily due to the error in our calculated unperturbed 3Π1-1Π energy separation.