Statistical equilibrium calculations of cometary molecules

Abstract

A model of the C2 molecule is proposed to explain the problems posed by the cometary C2 spectrum, and resonance fluorescence calculations are presented for other molecules observed in the UV spectra of comets. The physical model includes terms arising due to the intermixing of the vibrational levels of the X-prime and A-prime states of the C2 molecule in the statistical equilibrium equations. The model accounts for the greater intensities of the Swan bands arising from the triplet state with respect to the Phillips bands arising from the singlet state, and for the observed Swan band-sequence flux ratio. Calculations of resonance fluorescence are also found to be in good agreement with the properties of CO, CO(+), CN, CN(+), CS and OH lines in the UV spectra of comets West and Bradfield.