The Electronic Structure and Spectrum of RhC: New Bands in the 400–500 nm Region, Interacting 2Σ+ and 2Π States, and Deperturbation

Rhodium monocarbide (RhC) molecules were generated using a laser ablation/supersonic molecular beam source. Laser-induced and dispersed-fluorescence (DF) techniques were used to study the visible spectrum between 400 and 530 nm. Rh12C/Rh13C isotope shifts, DF, and excited level lifetime measurements assisted in classifying the observed bands into three series: the known C2Σ+ ← X2Σ+ system (short excited state lifetimes) and the two spin subsystems of a 2Πi ← X2Σ+ transition (long excited state lifetimes). A time-filtering technique was employed to separate effectively emission from close-lying 2Π and C2Σ levels. The C–X system is inherently strong; the 2Πi ← 2Σ+ system very weak. The 2Π1/2 ← 2Σ component is identified with the B–X system, previously taken to be of 2Σ+ ← 2Σ+ symmetry. The 2Π3/2 component gives rise to local perturbations in the C state. Many new bands in the 2Πi ← X2Σ+ transition were recorded and analyzed and the interactions/perturbations among the 2Σ+ and the newly established 2Πi states were examined in detail. We calculated many spectroscopic constants and other properties associated with the perturbed (mixed) levels of the 2Π1/2 and 2Σ+ states and compared them with the experimental data. In most of the comparisons, the calculated values are in quantitative agreement with the experimental ones. Calculations of the spin–rotation constants of the 2Σ+ and the Λ-doubling constants of the 2Π1/2 suggest the involvement of remote perturbers. Theory and experiment suggest that the electronic state labels of Scullman and Kaving [J. Mol. Spectrosc. 32, 475 (1969)], i.e., A2Πr, B2Σ+, C2Σ+, and D2Σ−, should be relabeled B2Πr, D2Π3/2, E2Σ+, and D2Π1/2, respectively.