THE COMETARY FLUORESCENCE-SPECTRUM OF CYANOGEN - A MODEL

We present a model to compute fluorescence spectra of the stable isotopes of CN in the comae of comets, The effects of collisions are included and shown to be significant as a mechanism secondary to the fluorescence process in the calculations. Our computed spectra are compared with high-resolution spectra of the B-2 Sigma(+)-X(2) Sigma(+) (0-0) band for comets Halley, Austin, and Levy. This comparison shows that collisional effects are observable in the CN spectra of relatively high production rate comets, such as Halley and Levy. Moreover, the model confirms that the overall structure of the CN spectra in comets results predominantly from pure fluorescence governed by the Swings effect. The primary goal of our model is to provide a methodology to compute accurate rotational line fluorescence efficiencies for the stable isotopes of CN: (CN)-C-12-N-14, (CN)-C-13-N-14, and (CN)-C-12-N-15. The fluorescence efficiencies are required to convert observed isotope line intensity ratios to isotope abundance ratios of carbon and nitrogen in comets.