Interstellar catalysis |
| |
| Authors: | Ronald G Tabak |
| |
| Institution: | (1) Dept. of Physics and Astronomy, Youngstown State University, Youngstown, Ohio, U.S.A. |
| |
| Abstract: | Since gas-phase reactions alone cannot account for the observed abundances of H2 in the typical interstellar cloud, one or more surface reactions are probably involved. Of the three possible candidates, only the catalytic production of H2 on transition metal grains is supported by laboratory evidence. Using the rate equations developed in a previous paper for this process, the steady-state equilibrium abundances of H, H2,e
–, H+, H–, H2
+, and H3
+ are calculated for large (r>10 pcs;M 102
M
 ), tenuous (n=102–104 cm–3) hydrogen dust clouds under a wide variety of conditions. In addition to the four rate equations involved in the catalytic reactions, 18 gas-phase and one additional surface reaction—the physical adsorption of H-atoms on cold, dielectric surfaces and their subsequent recombination and desorption as H2 molecules—are included in the calculations. It is found that metal grains can produce as much interstellar H2 as the best physical adsorption mechanism under optimum conditions if the extinction in the visible is less than 5m.0. The three critical parameters for efficient catalysis (activation energy of desorption, grain temperature, and the number density of available sites) are examined, and it is shown that catalytic reactions are efficient producers of H2 under all but the most unfavorable conditions. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
