Ab initio study of the PtC molecule. A new assignment of the red bands to the 1 3ΠΩ(Ω=1,0+)–X 1Σ+ transitions

Abstract

The electronic excited state spectrum of platinum monocarbide (PtC) was calculated by a multireference configuration interaction (MRCI) method with and without account of spin-orbit coupling (SOC). It is shown that the previous assignment of the red bands (700–880 nm) in the PtC spectrum should be changed from the singlet–singlet transitions A′ ¹Π–X ¹Σ⁺ and A″ ¹Σ⁺–X  ¹Σ⁺ to the singlet–triplet 1 ³Π_Ω–X ¹Σ⁺ transitions connected with two different spin sublevels (Ω=1,0⁺) of the lowest triplet 1 ³Π state. The previous assignment of the higher-lying excited states, A and B, is supported by the calculations. The A state corresponds to the singlet 1 ¹Π term. The first excited ¹Σ⁺ state corresponds to the observed B state and is responsible for a very intense UV band (306 nm). This state is strongly perturbed by SOC.