Rotational spectrum of ethyl cyanoacetylene (C₂H₅C≡C–C≡N), a compound of potential astrochemical interest

¹ Centre for Theoretical and Computational Chemistry (CTCC), Department of ChemistryUniversity of Oslo, PO Box 1033 Blindern 0315 Oslo Norway
e-mail: sophie.carles@kjemi.uio.no
² Permanent address: Institut de Physique de Rennes, Département de Physique Moléculaire, UMR 6251 UR1-CNRS, Université de Rennes 1, Bâtiment 11 C, Campus de Beaulieu, 35042 Rennes Cedex, France
³ Institut des Sciences Chimiques de Rennes, École Nationale Supérieure de Chimie de Rennes, CNRS, UMR 6226, 11 allée de Beaulieu CS 50837, 35708 Rennes Cedex 7, France

Received: 7 March 2013
Accepted: 8 June 2013

Abstract

Context. New radiotelescopes, such as the very sensitive ALMA, will enable the detection of interstellar molecules in much lower concentrations than previously possible. A successful identification of an interstellar molecule requires that laboratory microwave and millimeter-wave spectra are investigated. Several cyanopolyynes and alkynylcarbonitriles have already been detected in the interstellar medium (ISM). Cyanoacetylene (HC≡C–C≡N) is abundant in the ISM and its methyl derivative, 2-butynenitrile (CH₃C≡C–C≡N), is also present. The next derivative, ethyl cyanoacetylene, (2-pentynenitrile C₂H₅C≡C–C≡N) may also be present in interstellar space.

Aims. We report the rotational spectrum of the ethyl cyanoacetylene (C₂H₅C≡C–C≡N). This is hoped to facilitate identifying gaseous ethyl cyanoacetylene in the ISM.

Methods. We studied the rotational spectrum of C₂H₅C≡C–C≡N between 13 and 116 GHz with the microwave spectrometer of the University of Oslo. The spectroscopic study was augmented by high-level quantum-chemical calculations at B3LYP/cc-pVTZ and CCSD/cc-pVTZ levels of theory.

Results. We present for the first time the rotational spectrum of the ethyl cyanoacetylene (C₂H₅C≡C–C≡N). We assigned 342 transitions of the vibrational ground state, accurate values were obtained for rotational and centrifugal distortion constants, and the dipole moment was determined as well.