Other
Scientific paper
Aug 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997phdt.........4y&link_type=abstract
Thesis (PHD). HARVARD UNIVERSITY , Source DAI-B 58/02, p. 753, Aug 1997, 345 pages.
Other
10
Electron Degradation
Scientific paper
The thermal, chemical and ionizational structure of molecular gases subjected to various strengths of X-ray irradiation is investigated in detail. The investigation incorporate a detailed study of electron degradation in gas mixture of H2, H, He and He+ of varying fractional abundances. The influence of H2 vibrationally excited states on chemistry and thermal balance is analyzed. The diagnostic atomic and ionic line intensities and ratios and the H2 infrared emission are calculated in detail for different geometrical and physical conditions. The high energy X-rays are preferentially absorbed by He in pure H and He gases and gases with very low abundances of heavy elements, and by heavy elements in gases with solar abundances of heavy elements. The absorptions of X-rays produce fast photoelectrons which drive the chemistry and the heating process. The chemistry involves a network of about 1400 chemical reactions and about 150 species including all the major elements, and photodissociation and photoionization by X-ray induced H Lyα, and H2 Lyman-Werner photons are included. The heating is mainly through the X-ray induced fast photoelectron ionization, excitation, dissociation of H and H2 and Coulomb interactions; while the cooling channels include H recombination, free-free cooling, H collisional excitation cooling, H2 rovibrational cooling, collisional excitation of heavy element fine structure, metastable and allowed states, and OH, CO and H2O rovibrational states by electron, H and H2 impact cooling, and finally, gas grain collision cooling. The theoretical model is applied to the case of 1E 1740.7-2942, a hard X-ray source that lies in the direction of the Galactic Center. The theoretical and observational distributions of HCO+ J = 1-0 line intensity and CO and CS abundances of the molecular cloud in which 1E 1740.7-2942 may be embedded are in good agreement, which, in turn strongly supports the assertion that the hard X-ray source lies within the cloud near to its eastern edge. The intensities and distributions of HCO+ J = 3-2 and J = 4-3 emission lines are predicted, as are the abundances of other tracer species such as CN, NO, HCN.
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