A cometary Fluorescence Model for the ${\nu }_3$ Vibrational Band of Cyanogen

Abstract

Cyanogen (${\mathrm{C}}_2{\mathrm{N}}_2$) is suspected for a long time to be present in comets and to contribute to the creation of the CN radical. So far no observations with ground-based facilities have managed to detect this species but the Rosetta mission, thanks to in situ observations with the ROSINA mass spectrometer detected this species in the coma of 67P/Churyumov-Gerasimenko. To investigate its presence from infrared spectra in other comets, we developed a fluorescence model for the ${\nu }_3$ fundamental band. From new laboratory high-resolution infrared spectra of cyanogen, we analyzed the region of the ${\nu }_3$ band of ${\mathrm{C}}_2{\mathrm{N}}_2$, centered around 4.63 $\mu m$ (2158 $\mathrm{c}{\mathrm{m}}^{-1}$). In addition to line positions and intensities, molecular parameters for the ground and excited vibrational state were obtained. These parameters allowed us to develop a fluorescence model for cyanogen. Line-by-line excitation rates of the ${\nu }_3$ band of cyanogen in cometary comae are presented. An upper limit of the abundance of cyanogen in a spectrum of comet C/2022 E3 (ZTF) is discussed.