A fluorescence model of the C-3 radical in comets

Theoretical resonance fluorescence calculations are presented of the triato mic Cg radical and are compared with observations of the Cg emission in com ets Hale-Bopp and de Vice. A theoretical model of the C-3 vibration-rotatio nal structure in the A(1)II(u) - X(1)Sigma (+)(9) electronic system is intr oduced. The model takes into account the detailed structure of the bending mode nu (2) which is responsible for the emission of the 4050 Angstrom grou p. A total of 1959 levels are considered, with 515 levels in the ground sta te. The main effort is to model high-resolution spectra of the 4050 A emiss ion in comets C/1995 O1 Hale-Bopp and 122P/1995 S1 de Vice. The agreement b etween observed and theoretical spectra is good for a value of the dipole m oment derivative of d mu /dr approximate to 2.5 Debye Angstrom (-1). The mo deled C-3 emission exhibits a pronounced Swings effect.