Previously, we have observed the stabilization of the ground-state keto tautomer of 7-hydroxyquinoline (7HQ) in methanol/argon mixed matrices at 10 K. We ascribed the stabilized tautomer to the isolated 7HQ-(MeOH)(2) bridged complex on the basis of the observation that the open-chain methanol dimer concentration reaches a maximum concomitantly with the fluorescence excitation spectrum of the keto tautomer centered at 420 nm. Here, we report an increased stabilization of the ground-state keto tautomer when the open-chain CD3OD dimer is used and an additional increase upon photolysis. We also find that the use of the xenon matrix instead of argon inhibits the formation of the keto tautomer. We interpret these results in terms of a shift in the equilibria to favor the deuterated keto structure, due to the increase of hydrogen-bonding strength upon deuterium substitution. It becomes hindered in xenon, most probably due to a cage effect.