High-resolution spectra of C2 Swan bands from comet West 1976 VI

The present study of the comet West 1976 VI was intended to probe the C2 band structure by using sufficient spectral resolution to resolve the rotational structure of the bands. The study demonstrates that high-resolution spectra of the 0-0 Swan band provide an accurate determination of the C-12/C-13 ratio. The spectral resolution should, if possible, slightly exceed that employed on comet West. The conducted analysis of the C2 Swan Delta v = -1 sequence provides an excitation temperature of 3500 K for comet West at a heliocentric distance of 0.78 AU, which is considerably cooler than the vibrational temperature predicted by two recent calculations describing cometary C2 molecules bathed in sunlight.