Other
Scientific paper
Sep 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992mnras.258p..45p&link_type=abstract
Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 258, no. 2, Sept. 15, 1992, p. 45P-47P.
Other
39
Cosmic Rays, Dark Matter, Interstellar Chemistry, Interstellar Matter, Charge Transfer, Hydrogen Ions, Milky Way Galaxy, Molecular Clouds
Scientific paper
It is shown that there exist two phases in the chemical equilibrium state of dark interstellar clouds, according to the local value of the density, nH, and cosmic ray ionization rate, zeta. For a given value of zeta, the ion-neutral chemistry at high density is driven by proton transfer with H(3+), while at low density charge transfer with H(+) dominates. The transition between these two regimes occurs abruptly. Much higher values of the ratio n(C)/n(CO) are attained just below the critical density than just above it. The value of the critical density increases with zeta. When zeta = 2.5 x 10 exp -17/s, the transition occurs at nH equal or approximately equal to 10,000/cu cm. Thus the chemical equilibrium state of the gas may differ qualitatively from point to point in dark clouds or from one region to another in the Galaxy.
Flower David R.
Pineau des Forêts Guillaume
Roueff Evelyne
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