ner_tags: O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Telescope O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O
tokens: can also be seen for physisorption at very low temperature (≤6 K), when the grain can be full of immobile atoms (Katz et al. 1999 ). A corollary of this behavior is that in case the accretion is very efficient, the dust grain could have a large abundance (∼10 −6 ) of a particular species depending upon its desorption energy. For most species, this effect can lead to a change in the gas abundance phase profile. 6. Conclusions We have studied the chemistry of simple molecules on interstellar dust grains bound strongly by chemisorption on graphite. Chemical simulations involving chemisorbed and gas-phase species have been run for both isothermal and warm-up conditions using simplified assumptions. The isothermal models were run between 150 and 400 K at an interval of 25 K, and the warm-up models have a temperature range between 10 and 400 K. For each case, we have run models with different values of adsorption barriers and binding energies to explore the sensitivity of our results to these uncertain chemisorption parameters. Our major conclusions are as follows. 1. The efficiency of chemisorption hinges strongly on the efficiency of adsorption. Models having the lowest adsorption barrier for all species (0.1 eV) were found to produce reasonably abundant chemisorbed species, although the abundance of a chemisorbed species depends both on the adsorption rate and also other processes such as its chemistry. The reduction by a factor of 2 of individual desorption energies calculated by us does not increase the abundances markedly. 2. For species such as CO, which are very efficiently formed in the gas phase at almost all temperatures (10–400 K), the existence of chemisorbed molecules will not have a significant impact on their gas-phase abundances. However, some chemisorbed CO can be locked on grains, leading to a reasonably high abundance of ∼10 −6 , so that it could be detectable using upcoming observational facilities. Species such as C 2 H 2 and NH 3 , which are less efficiently formed in the gas phase compared with CO, may show a change in their gas-phase abundances due to chemisorption. The chemisorbed species can also approach peak abundances near ∼10 −6 and may be detectable. 3. A reasonably large number of chemisorbed species show fractional abundances above 10 −8 under certain conditions. An attempt to detect them using JWST might be worthwhile if chemisorbed species with higher abundances can be detected with reasonable signal to noise. 4. For warm-up models, if the efficiency of adsorption is high, a steplike abundance profile versus time is calculated using the assumption that chemisorption is possible only in the first monolayer, which rules out the formation of more than one layer. 5. Our calculations are based on the scant existing literature and simplified assumptions. In the future, detailed quantum mechanical calculations and experiments will be required to extract essential parameters such as diffusion barriers, sticking