title: Ultra-Broadband Dielectric and Optical Kerr-Effect Study of the Ionic Liquids Ethyl and Propylammonium Nitrate.
abstract: Dielectric relaxation (DR) and optical Kerr-effect (OKE) spectra of the archetypal protic ionic liquids ethyl- and propylammonium nitrate (EAN and PAN) have been measured over an unusually large frequency range from 200 MHz to 10 THz at temperatures (mostly) between 5 and 65 °C. Analysis of the low-frequency α-relaxation, associated with the cooperative relaxations of the cations (DR) and anions (OKE) and any clusters present, indicated that ion reorientation in EAN is decoupled from viscosity and occurs via cooperative relaxation involving large-angle jumps rather than rotational diffusion. Detailed consideration of the high-frequency parts of the DR and OKE spectra showed that the observed intensities were a complex combination of overlapping and possibly coupled modes. In addition to previously identified intermolecular H-bond vibrations, there are significant contributions from the librations of the cations and anions. The present assignments were shown to be consistent with the isotopic shifts observed for deuterated EAN.
authors.affiliation: †Institut für Physikalische und Theoretische Chemie, Universität Regensburg, Universitatsstr. 31, D-93040 Regensburg, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Sonnleitner
authors.affiliation: ‡School of Chemistry, University of Glasgow, University Avenue, Glasgow G12 8QQ, United Kingdom.
authors.forename: David A
authors.initials: DA
authors.lastname: Turton
authors.affiliation: §Chemistry Department, Murdoch University, Murdoch, W.A. 6150, Australia.
authors.forename: Glenn
authors.initials: G
authors.lastname: Hefter
authors.affiliation: ∥Department of Molecular and Optical Physics, Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Str. 3, 79104 Freiburg, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Ortner
authors.affiliation: ∥Department of Molecular and Optical Physics, Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Str. 3, 79104 Freiburg, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Waselikowski
authors.affiliation: ∥Department of Molecular and Optical Physics, Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Str. 3, 79104 Freiburg, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Walther
authors.affiliation: ‡School of Chemistry, University of Glasgow, University Avenue, Glasgow G12 8QQ, United Kingdom.
authors.forename: Klaas
authors.initials: K
authors.lastname: Wynne
authors.affiliation: †Institut für Physikalische und Theoretische Chemie, Universität Regensburg, Universitatsstr. 31, D-93040 Regensburg, Germany.
authors.forename: Richard
authors.initials: R
authors.lastname: Buchner