2014MNRAS.443.1301A

The temperature-programmed desorption spectra of H2 is recorded under ultrahigh vacuum conditions on an olivine substrate with more than 90 percent forsterite content for different coverage and temperatures. Then, using an empirical kinetic model, binding energy of H2 on the substrate is found to be 480±10K (41.36±0.86meV). Lower limit of sticking coefficient is estimated by comparing gas load at room temperature and at low temperature, which varies between 0.82 and 0.25 for temperatures between 7 and 14K. Using a gas-grain chemical network, it is found out that a steady state is reached around after 50 yr at 10K and both the steady-state abundance and time required to attend steady state is a strong function of temperature. Then, this model is used to check the effect of sticking of H2 on the grain surface chemistry. It is found that for H2O, CH4, NH3 and HCN, abundance due to reaction pathways involving H2 is within 1 percent, when compared with the abundance achieved considering most dominant pathways. Thus, neglecting sticking of H2 will not change overall abundance of these molecules. For carbon chain molecules, it was found that the reaction pathways with H2 may be important and could contribute significantly to account for the observed abundances. Since, sticking of H2 is temperature sensitive, increase in temperature will reduce the effect of these reactions.