title: Gas-Phase Infrared Spectroscopy of Substituted Cyanobutadiynes: Roles of the Bromine Atom and Methyl Group as Substituents.
abstract: The IR spectra of 5-bromo-2,4-pentadiynenitrile (Br-C≡C-C≡C-CN) and 2,4-hexadiynenitrile (CH3 -C≡C-C≡C-CN), a compound of interstellar interest, have been recorded within the 4000-500 cm(-1) spectral region and calculated by means of high-level ab initio and density functional calculations. Although the calculated structures of both compounds are rather similar, there are very subtle differences, mainly in the strength of the C≡C bond not directly bound to the substituent. These subtle bonding differences are reflected in small, but not negligible, differences in the electron density at the corresponding bond critical points, and, more importantly, are reflected in the IR spectra. Indeed, the IR spectrum for the bromine derivative presents two well-differentiated strong bands around 2250 cm(-1) , whereas for the methyl derivative both absorptions coalesce in a single band. These bands correspond in both cases to the coupling between C≡C and C≡N stretching displacements. A third, very weak, band also associated with C≡C and C≡N coupled stretches is observed for the bromine derivative, but not for the methyl one, owing to its extremely low intensity.
authors.affiliation: Departamento de Quimica, Modulo 13, Universidad Autonoma de Madrid, Campus de Excelencia UAM-CSIC, Cantoblanco, 28049, Madrid, Spain), Fax: (+34) 91-4975238. mm.montero@uam.es.
authors.forename: M Merced
authors.identifier: http://orcid.org/0000-0002-9499-0900
authors.initials: MM
authors.lastname: Montero-Campillo
authors.affiliation: Departamento de Quimica, Modulo 13, Universidad Autonoma de Madrid, Campus de Excelencia UAM-CSIC, Cantoblanco, 28049, Madrid, Spain), Fax: (+34) 91-4975238.
authors.forename: Otilia
authors.identifier: http://orcid.org/0000-0003-2596-5987
authors.initials: O
authors.lastname: Mó
authors.affiliation: Departamento de Quimica, Modulo 13, Universidad Autonoma de Madrid, Campus de Excelencia UAM-CSIC, Cantoblanco, 28049, Madrid, Spain), Fax: (+34) 91-4975238.
authors.forename: Manuel
authors.identifier: http://orcid.org/0000-0003-0854-585X
authors.initials: M
authors.lastname: Yáñez
authors.affiliation: Institut de Physique de Rennes, UMR 6251 CNRS, Université de Rennes 1, Campus de Beaulieu, 35042, Rennes Cedex, France. Abdessamad.benidar@univ-rennes1.fr.
authors.forename: Abdessamad
authors.initials: A
authors.lastname: Benidar
authors.affiliation: Institut des Sciences Chimiques de Rennes, Ecole Nationale Supérieure de Chimie de Rennes, CNRS, UMR 6226, 11 Allée de Beaulieu, CS 50837, 35708, Rennes Cedex 7, France.
authors.forename: Cédric
authors.identifier: http://orcid.org/0000-0002-1826-0666
authors.initials: C
authors.lastname: Rouxel
authors.affiliation: Institut des Sciences Chimiques de Rennes, Ecole Nationale Supérieure de Chimie de Rennes, CNRS, UMR 6226, 11 Allée de Beaulieu, CS 50837, 35708, Rennes Cedex 7, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Kerisit
authors.affiliation: Institut des Sciences Chimiques de Rennes, Ecole Nationale Supérieure de Chimie de Rennes, CNRS, UMR 6226, 11 Allée de Beaulieu, CS 50837, 35708, Rennes Cedex 7, France.
authors.forename: Yann
authors.initials: Y
authors.lastname: Trolez
authors.affiliation: Institut des Sciences Chimiques de Rennes, Ecole Nationale Supérieure de Chimie de Rennes, CNRS, UMR 6226, 11 Allée de Beaulieu, CS 50837, 35708, Rennes Cedex 7, France.
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Guillemin
keywords: IR spectroscopy; computational chemistry; cyanobutadiynes; density functional calculations; gas-phase studies