We present a combined theoretical and experimental study of the adsorption of two pairs
of organic isomers, (i) acetic acid AA (CH3COOH) and methyl
formate MF (HCOOCH3), and (ii) ethanol EtOH
(CH3CH2OH) and dimethyl ether DME (CH3OCH3),
onto crystalline water ice surfaces at low temperatures. Both approaches show that, for
each pair, the most stable isomer from a thermodynamical point of view,
i.e. AA and EtOH, is
also the one which is the more tightly bound to the water ice surface compared to the less
stable isomers (MF and DME). This finding, which can be explained by the ability of AA or
EtOH to efficiently interact with the ice surface via hydrogen bondings, may have
important consequences in an astrophysical context, since it could explain why the most
stable isomer is not the most abundant observed in the interstellar gas phase.