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

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 (CH 3 C≡C-C≡N), is also present. The next derivative, ethyl cyanoacetylene, (2-pentynenitrile C 2 H 5 C≡C-C≡N) may also be present in interstellar space. Aims. We report the rotational spectrum of the ethyl cyanoacetylene (C 2 H 5 C≡C-C≡N). This is hoped to facilitate identifying gaseous ethyl cyanoacetylene in the ISM. Methods. We studied the rotational spectrum of C 2 H 5 C≡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 (C 2 H 5 C≡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.

Gas phase basicities of polyfunctional molecules. Part 6: Cyanides and isocyanides

“…Cyanoacetylene, HCCCN, is a molecule of astrochemical interest; it has been detected in interstellar dark clouds, in comets, and in the atmosphere of Titan . By extension, its alkyl derivatives, 2‐butyne‐nitrile and 2‐pentyne‐nitrile, are also suspected to be present in interstellar space . The gas‐phase basicity of cyanoacetylene has been the subject of several experimental determinations (Table ).…”

“…94 By extension, its alkyl derivatives, 2-butynenitrile and 2-pentyne-nitrile, are also suspected to be present in interstellar space. 95 The gas-phase basicity of cyanoacetylene has been the subject of several experimental determinations 20,96-98 ( 77,98 (Table 9). A PA value of 751.2 kJ/mol has been retained in the NIST compilation.…”

Ab initio studies on cyanoacetylenes of astrochemical interest: [Y(CC)CN, Y C2H5, C3H7, C4H9, F, Cl, Br and CN]

“…In view of the above, in the present investigation in the gas phase, 72 the theoretical study performed by Carles et al (2013) (Khanna et al, 1987), one 82 of the moons of Saturn. However, it is yet to be found in the ISM and 83 it was also postulated by Woon and Herbst (2009) …”

“…The C 2 H 5 rad-307 ical produced by reaction (4.6) can produce C 4 H 10 radical through 308 radical-radical association: 309 C 2 H 5 +C 2 H 5 →C 4 H 10 (4.10) accompanied by neutral-neutral reaction with (C≡C)CN radical: 310 C 4 H 10 +(C≡C) CN→C 4 H 9 (C≡C) CN+H (4.11) Similar reaction paths to (4.7) and (4.9) were suggested by Carles 311 et al (2013) for C 2 H 5 (C≡C)CN, but the source of C 2 H 5 radical was 312 not specified, unlike in this work. Carles et al (2013) attributed the 313 unidentification of the C 2 H 5 radical in the ISM to its small dipole mo-314 ment, as evidenced by the work of Rudić et al (2004). Carles et al 315 (2013) also predicted two other possible formation mechanisms for 316 C 2 H 5 (C≡C)CN, although they involve unidentified precursor species.…”

“…The cyano (C≡N) functional group, found in neutral molecules, 2 radicals and ions, is extremely prevalent in the interstellar medium 3 (ISM) and other extraterrestrial regions (Ehrenfreund and Charnley,4 2000; Bernstein et al, 2004;Carles et al, 2013). Cyanoacetylene, 5 H(C≡C)CN, has been a known interstellar molecule for a long 6 time (Turner, 1971) and a precursor to biomolecules found in ISM 7 (Majumdar et al, 2012).…”