[PCG23-P02] Theory of Self-induced Desorption of Molecules from Cold Dust Surface
Keywords:Astrochemistry, Molecular cloud, Grain-surface reaction, Desorption
We propose a new mechanism that is necessarily associated with exothermic reactions of molecules on grain surfaces even in cold environments like cold dense cores of molecular clouds. This mechanism consists of three steps that occur on the grain surface: (1) formation of new molecules by an exothermal grain-surface reaction, (2) heating of the dust surface due to release of the heat of formation, and (3) desorption of the newly formed molecules into the gas phase.
We formulate the desorption probability of molecules newly formed by exothermic reaction by calculating the temperature distribution on the grain surface as a function of the distance from the reaction site and time. Our formula of desorption probability P is a function of heat of formation Q, desorption energy Ed of a molecule from a substrate, and molecular weight μ of a desorbing molecule. We compare P with the experiments for reactions of various Q, Ed, and μ for three substrates of oxidized HOPG, nonporous amorphous water ice, and amorphous silicate. Here, we used the compilation of the experimental data by Minissale et al. (2016). We also show a method developed for the comparison of our theory with the experiments. Discussion is given on the comparison of our theory with other two theories of desorption (Garrod et al., 2007; Minissale et al., 2016).