title: Tunable diode lasers as a tool for conformational control: the case of matrix-isolated oxamic acid.
abstract: A tunable diode laser was applied as a source of narrowband near-infrared light used to manipulate the structure of the molecule of oxamic acid. Monomers of the most stable conformer I of the molecule, with the trans orientation of the O═COH group and the trans orientation of the O═CC═O fragment, were trapped from the gas phase in low-temperature argon, neon, and nitrogen matrixes. Monomers of oxamic acid, isolated in argon or neon matrixes, were then irradiated with narrowband near-IR light from the diode laser tuned at 6833 (Ar) or 6840 cm(-1) (Ne). Upon such irradiation another conformer, II, of oxamic acid was generated, with cis orientation of the O═COH group and trans orientation of the O═CC═O fragment. Both forms were identified by comparison of their experimental mid-IR spectra with the spectra theoretically calculated for I and II. Subsequent irradiation of the matrix at 6940 (Ar) or 6991 cm(-1) (Ne), where absorption appeared in the near-IR spectrum of the photoproduct, led to photoconversion of conformer II into form I. In a series of subsequent irradiations at 6833(Ar)/6840(Ne) cm(-1) and at 6940(Ar)/6991(Ne) cm(-1), the population of oxamic acid molecules was selectively shifted several times from I to II and vice versa. As far as we know, this is the first reported study where a tunable diode laser source of narrowband near-IR light was used to manipulate the structure of a molecule. Spontaneous II → I transformation was observed for Ne and Ar matrixes kept in the dark and at cryogenic temperature.
authors.affiliation: †Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland.
authors.forename: Anna
authors.initials: A
authors.lastname: Halasa
authors.affiliation: †Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland.
authors.forename: Leszek
authors.initials: L
authors.lastname: Lapinski
authors.affiliation: †Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland.
authors.forename: Hanna
authors.initials: H
authors.lastname: Rostkowska
authors.affiliation: ‡Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
authors.forename: Igor
authors.initials: I
authors.lastname: Reva
authors.affiliation: †Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland.
authors.forename: Maciej J
authors.initials: MJ
authors.lastname: Nowak