title: (1)H-(17)O nuclear-quadrupole double-resonance study of hydrogen disorder in 2-nitrobenzoic acid.
abstract: Temperature dependence of (17)O nuclear quadrupole resonance frequencies was measured in solid 2-nitrobenzoic acid by a (1)H-(17)O nuclear quadrupole double resonance technique. The experimental results show the presence of a fast exchange of hydrogen atoms between two nonequivalent positions within the O-H ellipsis O hydrogen bonds. The hydrogen disorder is ascribed to concerted jumps of two hydrogen atoms within the hydrogen bonds connecting two molecules in a dimer. The energy difference DeltaE of the two hydrogen configurations is equal to DeltaE = 60 meV = 5.8 kJ/mol. The dipole structure of the (17)O NQR lines from the C-O-H oxygen positions was also measured at -100 degrees C and at room temperature. The orientation of the principal axes of the electric field gradient tensor with respect to the O-H bond and the sign of the quadrupole coupling constant were determined. The oxygen-hydrogen distance R(O-H), as determined from the dipole structure of the (17)O NQR lines is at -100 degrees C equal to 0.099 nm. At room temperature we observe a longer distance, R(O-H) = 0.101 nm, in agreement with the hydrogen intrabond exchange.
authors.affiliation: Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana, Slovenia.
authors.forename: M
authors.initials: M
authors.lastname: Torkar
authors.forename: V
authors.initials: V
authors.lastname: Zagar
authors.forename: J
authors.initials: J
authors.lastname: Seliger
mesh_terms: D001565:Benzoates / Q000737:chemistry*; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008433:Mathematics; D015394:Molecular Structure; D010104:Oxygen Radioisotopes; D013696:Temperature
chemical_list: D001565:Benzoates; D010104:Oxygen Radioisotopes