title: Contrasting Effects of Water on the Barriers to Decarboxylation of Two Oxalic Acid Monohydrates: A Combined Rotational Spectroscopic and Ab Initio Study.
abstract: Using rotational spectroscopy, we have observed two isomers of the monohydrate of oxalic acid, the most abundant dicarboxylic acid in the atmosphere. In the lowest-energy isomer, water hydrogen-bonds to both carboxylic acid groups, and the barrier to decarboxylation decreases. In the second isomer, water bonds to only one carboxylic acid group, and the barrier increases. Though the lower barrier in the former is not unequivocal evidence that water acts as a photocatalyst, the higher barrier in the latter indicates that water acts as an inhibitor in this topology. Oxalic acid is unique among dicarboxylic acids: for the higher homologues calculated, the inhibiting topology of the monohydrate is lowest in energy and most abundant under atmospheric conditions. Consequently, oxalic acid is the only dicarboxylic acid for which single-water catalysis of overtone-induced decarboxylation in the atmosphere is plausible.
authors.affiliation: Department of Chemistry, University of Alberta , Edmonton, Alberta T6G 2G2, Canada.
authors.forename: Elijah G
authors.initials: EG
authors.lastname: Schnitzler
authors.affiliation: Department of Chemistry, University of Alberta , Edmonton, Alberta T6G 2G2, Canada.
authors.forename: Courtenay
authors.initials: C
authors.lastname: Badran
authors.affiliation: Department of Chemistry, University of Alberta , Edmonton, Alberta T6G 2G2, Canada.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Jäger