Abstract :
Irvine et al. [Irvine, W.M., Senay, M., Lovell, A.J. et al. Note: Detection of nitrogen sulfide in Comet Hale-Bopp, Icarus, 143, 412–414, 2000] observed the nitrogen monosulfide radical (NS) in Comet Hale-Bopp, through the rotational transition J = 15/2–13/2, in the vibrational level v″ = 0, of the fundamental electronic state X2Πr. This was the first time ever that this radical was observed in comets. With their observational data and considering an optically thin coma, Irvine et al. [Irvine, W.M., Senay, M., Lovell, A.J. et al. Note: Detection of nitrogen sulfide in Comet Hale-Bopp, Icarus, 143, 412–414, 2000] determined the colunar abundance in the coma and the production rate of this species. Until the present time, the lifetime of NS against photodissociation is unknown in Literature. In order to determine the production rate of this radical they applied a Haser model, using lifetimes associated to the analogous isoelectronic species NO. Following Lie et al. [Lie, G.C., Peyerimhoff, S.D., Buenker, R.J. Configuration interaction studies of low-lying valence and Rydberg states of NS, J. Chem. Phys., 82, 2672–2678, 1985], the NS radical dissociates for λ = 2305.37 Å, which corresponds to the (v′ = 0 → v″ = 0) vibrational band of the NS(C2Σ+–X2Πr) electronic system. Considering the rotational and vibrational constants [Huber, K.P., Herzberg, G. Constants of Diatomic Molecules, Van Nostrand, New York, 1979] for these electronic states we determine the associated r-centroids and Franck–Condon factors. With these values and the electronic transition moments, extrapolated from the values of Lie et al. [Lie, G.C., Peyerimhoff, S.D., Buenker, R.J. Configuration interaction studies of low-lying valence and Rydberg states of NS, J. Chem. Phys., 82, 2672–2678, 1985], we determine the spontaneous emission rates image and the absorption oscillator strengths image of several vibrational bands of that electronic system for this species. The Einstein’s coefficient for absorption of the relevant vibrational band (0, 0), combined with the solar fluxes (maximum and minimum), for λ = 2305.37 Å and heliocentric distance rh = 1.0 AU, allowed us to determine the photodissociation rate in this electronic system and the concerning lifetimes. We also determine the g-factors of fluorescence efficiency. Finally, with the photodissociation lifetimes and the g-factors for the NS radical, we re-evaluate the production rate of the species and compare our results with Irvine et al. [Irvine, W.M., Senay, M., Lovell, A.J. et al. Note: Detection of nitrogen sulfide in Comet Hale-Bopp, Icarus, 143, 412–414, 2000] finding a good agreement.
