Chlorine chemistry as a possible source of ionization of interstellar hydrogen

Details Chlorine chemistry as a possible source of ionization of interstellar hydrogen Chlorine chemistry as a possible source of ionization of interstellar hydrogen

Mar 1979

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979mnras.186..621q&link_type=abstract

Monthly Notices of the Royal Astronomical Society, vol. 186, Mar. 1979, p. 621-632.

Other

2

Chlorine, Gas Ionization, Hydrogen Clouds, Interstellar Chemistry, Interstellar Gas, Chemical Equilibrium, Chemical Reactions, Ion Production Rates, Molecular Gases, Photodissociation

Scientific paper

Following a conjecture of Jura we work out below the details of the reactions Cl II + H2 = HCl II + H and photo-dissociation HCl II + hv = H II + Cl, as a source for the production of H II in the interstellar medium. This idea is then applied to the cloud of NGC 2024. To that end chemical and ionization equilibria are set up to determine the number densities of various constituents of Cl and of C II, H II, Mg II, Si II, SII and Fe II. Calculations are performed for nH = 5 × 103, 104, 2 × 104 and 5 × 104 cm-3, and the effects of the molecular formation rate R and those of dust optical depths τd on emission measures are studied.
It is found that, for instance, when nH = 104, R = 10-17 cm-3 s-1 and τd = 4.5 × 10-3 nHχ or 1.5 × 10-3 nHχ (where χ is the cloud depth in parsecs) the ratio EM(H+)/EM(C+) agrees fairly well with the observed range of intensity ratio 0.3 0.6. Such ratios of emission measures for other elements heavier than carbon are also presented and discussed. The neutral hydrogen column densities are also found to agree with that observed, 3 × 1021 cm-2.
This study shows that a cool H I region of narrow hydrogen lines lies in between the C II and H II regions, sharing some portion with the C II region but slightly displaced towards the outer boundary of the H II region. This finding is in agreement with the recently found small velocity difference which is slightly shifted towards the central velocity of the H II region (Pankonian et al.).

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