Emission and laser-excitation spectra of the ≈A2Π ? ≈X2Π transition of rotationally cooled bromochloroacetylene cation in the gas phase

Rotationally cooled bromochloroacetylene cations have been studied in the ≈X²Π_ω and ≈A²Π_ω (ω = $\text{3}\text{2}$, $\text{1}\text{2}$) states in the gas phase by two complementary spectroscopic techniques. The ≈A²Π ? ≈X²π band system was excited in emission by electron impact of a seeded supersonic helium free jet and as fluorescence by laser excitation of cations formed by Penning ionisation in a cooled environment. Comparison of the two sets of data locates the spin—orbit component bands and the origins of the systems, and allows the main spectral features to be vibronically assigned. The vibrational frequencies of most of the fundamentals are thus obtained to within ±2 cm^?1 for this cation in both the states.