title: Infrared characterization of the HCOOH···CO2 complexes in solid argon: stabilization of the higher-energy conformer of formic acid.
abstract: The complexes of formic acid (HCOOH, FA) with carbon dioxide are studied by infrared spectroscopy in an argon matrix. Two trans-FA···CO(2) and one cis-FA···CO(2) complexes are experimentally identified while the calculations at the MP2(full)/6-311++G(2d,2p) level of theory predict one more minimum for the cis-FA···CO(2) complex. The complex of the higher-energy conformer cis-FA with CO(2) is prepared by vibrational excitation of the ground-state trans-FA conformer combined with thermal annealing. The lifetime of the cis-FA···CO(2) complex in an argon matrix at 10 K is 2 orders of magnitude longer than that of the cis-FA monomer. This big difference is explained by the computational results which show a higher stabilization barrier for the complex. The solvation effects in solid argon are theoretically estimated and their contribution to the stabilization barriers of the higher-energy species is discussed. The relative barrier transmissions for hydrogen tunneling in the cis-FA···CO(2) complex and cis-FA monomer are in good agreement with the experimental decay rates.
authors.affiliation: Department of Chemistry, University of Helsinki, P.O. Box 55, FIN-00014, Finland. masashi.tsuge@helsinki.fi
authors.forename: Masashi
authors.initials: M
authors.lastname: Tsuge
authors.forename: Kseniya
authors.initials: K
authors.lastname: Marushkevich
authors.forename: Markku
authors.initials: M
authors.lastname: Räsänen
authors.forename: Leonid
authors.initials: L
authors.lastname: Khriachtchev