Fourier transform UV, visible, and infrared spectra of supersonically cooled CN radical

The CN radical has been observed by Fourier transform spectroscopy in the ultraviolet, visible, and infrared regions of the spectrum. The radical was formed in a corona discharge of acetonitrile seeded in an inert carrier gas (helium or argon) at the throat of a pinhole nozzle and expanded into the vacuum chamber. The emission was resolved with a Bruker IFS-120 HR spectrometer. The B-X and A-X electronic transitions were observed from approximately 27 000 to 2500 cm^-1. The B-X 0-0 band exhibited an anomalous rotational intensity distribution which cannot be described by a simple rotational temperature. This provides insight into the mechanisms of CN formation in our source. Vibrational levels up to v = 15 in both electronic states are observed. Such high vibrational excitation would require temperatures near 10 000 K. The population distribution appears nearly Boltzmann for low vibrational levels, albeit a high temperature, and deviates markedly at high vibrational levels.