Enhanced production of HD and D_2 molecules on small dust grains in diffuse clouds

摘要

Motivated by recent observations of deuterated molecules in the interstellarmedium, we examine the production of HD and D$_2$ molecules on dust grainsurfaces. A mechanism for the enhanced production of these deuterated moleculesis studied. This mechanism applies on grain surfaces on which D atoms stickmore strongly than H atoms, under conditions of low flux and within a suitablerange of temperatures. It is shown that under these conditions the productionrates of HD and D$_2$ are greatly enhanced (vs. the H$_2$ production rate)compared with the expected rates based on the adsorption of gas-phase atomicabundances of D and H. The enhancement in the formation rate of HD iscomparable with the enhancement due to gas-phase ion-molecule reactions indiffuse clouds.