The Effect of H$$_2$$O and Electron Collisions on Rotational Populations of Cometary CO

Abstract

We present a simple model of CO excitation in comets, including solar pumping, ro-vibrational (de)excitation by H2O and electron collisions, and fluorescence. Collisional data for H2O−CO are taken from quantum statistical calculations while Born dipole cross-sections are calculated for electron-CO collisions. In the non-LTE regime, i.e. at H2O densities in the range 10 3 − 10 8 cm −3 , CO excitation is found to be largely dominated by H2O collisions, with electron collisions becoming significant only for density profiles with scaling factors xn e > 3.