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Context. The abundances of many observed compounds in interstellar molecularclouds still lack an explanation, despite extensive research that includes bothgas and solid (dust-grain surface) phase reactions. Aims. We aim toqualitatively prove the idea that a hydrogen-poor subsurface chemistry oninterstellar grains is responsible for at least some of these chemical"anomalies". This chemistry develops in the icy mantles when photodissociationreactions in the mantle release free hydrogen, which escapes the mantle viadiffusion. This results in serious alterations of the chemical composition ofthe mantle because pores in the mantle provide surfaces for reactions in thenew, hydrogen-poor environment. Methods. We present a simple kinetic model,using existing astrochemical reaction databases. Gas phase, surface andsubsurface pore reactions are included, as are physical transformations ofmolecules. Results. Our model produces significantly higher abundances forvarious oxidized species than most other models. We also obtain quite goodresults for some individual species that have adequate reaction network. Thus,we consider that the hydrogen-poor mantle chemistry may indeed play a role inthe chemical evolution of molecular clouds. Conclusions. The significance ofoutward hydrogen diffusion has to be proved by further research. A huge numberof solid phase reactions between many oxidized species is essential to obtaingood, quantitative modeling results for a comparison with observations. Wespeculate that a variety of unobservable hydrogen-poor sulfur oxoacidderivatives may be responsible for the "disappearance" of sulfur in dark cloudcores.

Subsurface chemistry of mantles of interstellar dust grains in dark molecular cores