THE STATES OF CARBON AND NITROGEN-ATOMS AFTER PHOTODISSOCIATION OF CN, CH, CH+, C2, C3, AND CO IN COMETS

Solar ultraviolet radiation leads to photodissociation of cometary CN, CH, CH+, C2, C3, and CO and is a source of the CI lines at wavelengths λ = 156.1, 165.7, and 193.1 nm and the CII line at λ = 133.5 nm found in the ultraviolet spectra of several comets. Photodissociation of CN occurs in the wavelength range 83-108 nm and is a source of metastable NI (2D0) and NI (2P0) atoms in comets. Emission at λ = 149.3 nm of the NI (2P-2D0) transition may be caused by the resonance fluorescence mechanism and may be observable in comets at heliocentric distances r < 0.25 AU. © 1991.