The charge state in a highly dense molecular cloud

Details The charge state in a highly dense molecular cloud The charge state in a highly dense molecular cloud

Apr 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992ap%26ss.190..257e&link_type=abstract

Astrophysics and Space Science (ISSN 0004-640X), vol. 190, no. 2, April 1992, p. 257-270.

Astronomy and Astrophysics

Astrophysics

4

Charged Particles, Interstellar Matter, Molecular Clouds, Molecular Ions, Cosmic Dust, Electron Emission, Magnetic Flux, Ohmic Dissipation, Thermionic Emission

Scientific paper

The desorption rates were calculated of both physisorbed and chemisorbed ions from grain surfaces, due to the temperature increase at densities higher than 10 exp -13 g/cu cm. It has been found that physisorbed ions desorb from grain surfaces at neutral densities of n greater than 1.3 x 10 exp 11/cu cm, assuming that the desorption energy D is equal to 0.1 eV, while the desorption of chemisorbed ions from grain surface can only occur at neutral densities of n greater than 10 exp 15/cu cm, at which point thermal ionization becomes more dominant. The electrons are assumed to be emitted from grain surfaces in a manner similar to the thermionic emission from heated solid surfaces. It was found that the temperature at which electrons are emitted from negatively charged grains depends on the value of the work function of the material of the grain. The charge state has been calculated for two limiting cases. Neglecting the grain surface reactions in case one, the resulting relative charge density represents an upper limit, such that the electrical conductivity remains high. In this situation the magnetic flux dissipation is mainly contributed by ambipolar diffusion. In the second case, it has been assumed that the charged particles are chemically adsorbed on grain surfaces such that their desorption is negligible. In this case, the charge density decreases sharply with increase of neutral density. Therefore, the electrical conductivity decreases sufficiently and ohmic dissipation becomes effective.

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