Open AccessMonte Carlo simulations of H 2 formation on stochastically heated grains
Author(s) -
Cuppen H. M.,
Morata O.,
Herbst Eric
Publication year - 2006
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2006.10079.x
Subject(s) - physics , monte carlo method , hydrogen , surface finish , evaporation , photon , grain size , surface roughness , chemical physics , molecular physics , computational physics , optics , materials science , thermodynamics , quantum mechanics , statistics , mathematics , metallurgy , composite material
Continuous‐time, random‐walk Monte Carlo simulations of H 2 formation on grains have been performed for surfaces that are stochastically heated by photons. We have assumed diffuse cloud conditions and used a variety of grains of varying roughness and size based on olivine. The simulations were performed at different optical depths. We confirmed that small grains ( r ≤ 0.02 μm) have low modal temperatures with strong fluctuations, which have a large effect on the efficiency of the formation of molecular hydrogen. The grain size distribution highly favours small grains and therefore H 2 formation on these particles makes a large contribution to the overall formation rate for all but the roughest surfaces. We find that at A V = 0 only the roughest surfaces can produce the required amount of molecular hydrogen, but by A V = 1 , smoother surfaces are possible alternatives. Use of a larger value for the evaporation energy of atomic hydrogen, but one still consistent with experiment, allows smoother surfaces to produce more H 2 .