Deperturbation study of the d3Πg,v′=4 state of C2 by applying degenerate and two-color resonant four-wave mixing

The potential of four-wave mixing spectroscopy in combination with a discharge slit-jet source is explored by performing an analysis of the perturbations occurring between vibronic levels of the d3Πg,v′=4 and b3Σg-,v′=16 states of C2. Unambiguous assignments of perturbed transitions are achieved by intermediate level labeling in the a3Πu state of the Swan system and results in the re-assignment of several line positions found in the literature. Furthermore, extra transitions are observed and assigned in a straightforward manner that originate from the perturbing b3Σg-,v′=16 electronic state. Significantly perturbed rotational transitions in the (4, 3) band of the Swan system are reported for the first time. A least-squares fit to 35 perturbed and perturbing transitions yields the vibronic origin, rotational and spin-spin coupling constant of the b3Σg-,v′=16 state as well as the spin-orbit and L-uncoupling parameters for the interaction between the d3Πg,v′=4 and b3Σg-,v′=16 states.