title: Rotation-vibration interactions in the spectra of polycyclic aromatic hydrocarbons: Quinoline as a test-case species.
abstract: Polycyclic aromatic hydrocarbons (PAHs) are highly relevant for astrophysics as possible, though controversial, carriers of the unidentified infrared emission bands that are observed in a number of different astronomical objects. In support of radio-astronomical observations, high resolution laboratory spectroscopy has already provided the rotational spectra in the vibrational ground state of several molecules of this type, although the rotational study of their dense infrared (IR) bands has only recently become possible using a limited number of experimental set-ups. To date, all of the rotationally resolved data have concerned unperturbed spectra. We presently report the results of a high resolution study of the three lowest vibrational states of quinoline C9H7N, an N-bearing naphthalene derivative. While the pure rotational ground state spectrum of quinoline is unperturbed, severe complications appear in the spectra of the ν45 and ν44 vibrational modes (located at about 168 cm(-1) and 178 cm(-1), respectively). In order to study these effects in detail, we employed three different and complementary experimental techniques: Fourier-transform microwave spectroscopy, millimeter-wave spectroscopy, and Fourier-transform far-infrared spectroscopy with a synchrotron radiation source. Due to the high density of states in the IR spectra of molecules as large as PAHs, perturbations in the rotational spectra of excited states should be ubiquitous. Our study identifies for the first time this effect and provides some insights into an appropriate treatment of such perturbations.
authors.affiliation: AILES Beamline, Synchrotron SOLEIL, l'Orme des Merisiers, Saint-Aubin, 91192 Gif-sur-Yvette cedex, France.
authors.forename: O
authors.initials: O
authors.lastname: Pirali
authors.affiliation: Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland.
authors.forename: Z
authors.initials: Z
authors.lastname: Kisiel
authors.affiliation: Laboratoire de Physique des Lasers, Atomes et Molécules, UMR 8523 CNRS - Université Lille 1, Bâtiment P5, F-59655 Villeneuve d'Ascq Cedex, France.
authors.forename: M
authors.initials: M
authors.lastname: Goubet
authors.affiliation: AILES Beamline, Synchrotron SOLEIL, l'Orme des Merisiers, Saint-Aubin, 91192 Gif-sur-Yvette cedex, France.
authors.forename: S
authors.initials: S
authors.lastname: Gruet
authors.affiliation: Laboratoire de Physico-Chimie de l'Atmosphère, EA-4493, Université du Littoral - Côte d'Opale, 59140 Dunkerque, France.
authors.forename: M A
authors.initials: MA
authors.lastname: Martin-Drumel
authors.affiliation: Laboratoire de Physico-Chimie de l'Atmosphère, EA-4493, Université du Littoral - Côte d'Opale, 59140 Dunkerque, France.
authors.forename: A
authors.initials: A
authors.lastname: Cuisset
authors.affiliation: Laboratoire de Physico-Chimie de l'Atmosphère, EA-4493, Université du Littoral - Côte d'Opale, 59140 Dunkerque, France.
authors.forename: F
authors.initials: F
authors.lastname: Hindle
authors.affiliation: Laboratoire de Physico-Chimie de l'Atmosphère, EA-4493, Université du Littoral - Côte d'Opale, 59140 Dunkerque, France.
authors.forename: G
authors.initials: G
authors.lastname: Mouret