title: CW- and pulsed-EPR of carbonaceous matter in primitive meteorites: solving a lineshape paradox.
abstract: Insoluble organic matter (IOM) of Orgueil and Tagish Lake meteorites are studied by CW-EPR and pulsed-EPR spectroscopies. The EPR line is due to polycyclic paramagnetic moieties concentrated in defect-rich regions of the IOM, with concentrations of the order of 4x10(19) spin/g. CW-EPR reveals two types of paramagnetic defects: centres with S=1/2, and centres with S=0 ground state and thermally accessible triple state S=1. In spite of the Lorentzian shape of the EPR and its narrowing upon increasing the spin concentration, the EPR line is not in the exchange narrowing regime as previously deduced from multi-frequency CW-EPR [L. Binet, D. Gourier, Appl. Magn. Reson. 30 (2006) 207-231]. It is inhomogeneously broadened as demonstrated by the presence of nuclear modulations in the spin-echo decay. The line narrowing, similar to an exchange narrowing effect, is the result of an increasing contribution of the narrow line of the triplet state centres in addition to the broader line of doublet states. Hyperfine sublevel correlation spectroscopy (HYSCORE) of hydrogen and (13)C nuclei indicates that IOM* centres are small polycyclic moieties that are moderately branched with aliphatic chains, as shown by the presence of aromatic hydrogen atoms. On the contrary the lack of such aromatic hydrogen in triplet states suggests that these radicals are most probably highly branched. Paramagnetic centres are considerably enriched in deuterium, with D/H approximately 1.5+/-0.5x10(-2) of the order of values existing in interstellar medium.
authors.affiliation: CNRS, Ecole Nationale Supérieure de Chimie de Paris (ENSCP, ParisTech), Laboratoire de Chimie de la Matière Condensée de Paris, UMR-CNRS 7574, 11 rue Pierre et Marie Curie, 75231 Paris Cedex 05, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Delpoux
authors.forename: Didier
authors.initials: D
authors.lastname: Gourier
authors.forename: Laurent
authors.initials: L
authors.lastname: Binet
authors.forename: Hervé
authors.initials: H
authors.lastname: Vezin
authors.forename: Sylvie
authors.initials: S
authors.lastname: Derenne
authors.forename: François
authors.initials: F
authors.lastname: Robert
mesh_terms: D002244:Carbon / Q000737:chemistry*; D002247:Carbon Isotopes; D003903:Deuterium; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D005618:Fresh Water; D008280:Magnetics; D019110:Meteoroids; D012995:Solubility; D013696:Temperature
chemical_list: D002247:Carbon Isotopes; D002244:Carbon; D003903:Deuterium