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/supersonic molecular beam source. Laser-induced and dispersed-fluorescence (DF) techniques were used to study the visible spectrum between 400 and 530 nm. Rh(12)C/Rh(13)C isotope shifts, DF, and excited level lifetime measurements assisted in classifying the observed bands into three series: the 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 (long excited state lifetimes). A time-filtering technique was employed to separate 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 system, 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 new bands in the (2)Pi(i) <-- X(2)Sigma(+) transition were recorded and analyzed and the interactions/perturbations among the (2)Sigma(+) and the newly established (2)Pi(i) states were examined in detail. We calculated many spectroscopic constants and other properties associated with the perturbed (mixed) 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 are in quantitative agreement with the experimental ones. Calculations of the spin-rotation constants of the (2)Sigma(+) and the Lambda-doubling constants of the (2)Pi(1/2) 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., A(2)Pi(r), B(2)Sigma(+), C(2)Sigma(+), and D(2)Sigma(-), should be relabeled B(2)Pi(r), D(2)Pi(3/2), E(2)Sigma(+), and D(2)Pi(1/2), respectively. Copyright 1999 Academic Press.