The electronic structure and spectrum of RhC: New bands in the 400-500 nm region, interacting (2)Sigma(+) and (2)Pi states, and deperturbation

Rhodium monocarbide (RhC) molecules were generated using a laser ablation/s upersonic molecular beam source. Laser-induced and dispersed-fluorescence ( DF) techniques were used to study the visible spectrum between 400 and 530 nm. (RhC)-C-12/(RhC)-C-13 isotope shifts, DF, and excited level lifetime me asurements assisted in classifying the observed bands into three series: th e known C(2)Sigma(+) --> X(2)Sigma(+) system (short excited state lifetimes ) and the two spin subsystems of a (2)Pi(i) <-- X(2)Sigma(+) transition (lo ng excited state lifetimes). A time-filtering technique was employed to sep arate effectively emission from close-lying (2)Pi and C(2)Sigma levels. The C-X system is inherently strong; the (2)Pi(i) <-- (2)Sigma(+) system very weak. The (2)Pi(1/2) <-- (2)Sigma component is identified with the B-X syst em, previously taken to be of (2)Sigma(+) <-- (2)Sigma(+) symmetry. The (2) Pi(3/2) component gives rise to local perturbations in the C state. Many ne w bands in the (2)Pi(i) <-- X(2)Sigma(+) transition were recorded and analy zed and the interactions/perturbations among the (2)Sigma(+) and the newly established (2)Pi(i) states were examined in detail. We calculated many spe ctroscopic constants and other properties associated with the perturbed (mi xed) levels of the (2)Pi(1/2) and (2)Sigma(+) states and compared them with the experimental data. In most of the comparisons, the calculated values a re in quantitative agreement with the experimental ones. Calculations of th e spin-rotation constants of the (2)Sigma(+) and the R-doubling constants o f the (2)Pi(1/2) suggest the involvement of remote perturbers. Theory and e xperiment suggest that the electronic state labels of Scullman and Kaving [ J. Mol. Spectrosc. 32, 475 (1969)], i.e., A(2)Pi(r), B(2)Sigma(+), C(2)Sigm a(+), and D(2)Sigma(-), Should be relabeled B(2)Pi(r), D(2)Pi(3/2), E(2)Sig ma(+), and D(2)Pi(1/2), respectively. (C) 1999 Academic Press.