EDP Sciences logo
Subscriber Authentication Point
Search
Menu
Home All issues Volume 558 (October 2013) A&A, 558 (2013) A6 Full HTML
Free Access
Issue
A&A
Volume 558, October 2013
Article Number A6
Number of page(s) 12
Section Atomic, molecular, and nuclear data
DOI https://doi.org/10.1051/0004-6361/201321427
Published online 26 September 2013

© ESO, 2013

1. Introduction

About 180 molecules, ions, and radicals have been detected in the interstellar medium (ISM) and circumstellar shells. The vast majority of these species have been identified by means of their rotational spectra. As many as about 25 of these compounds contain the cyano group (C≡N). This group is not only found in neutral molecules, but also in radicals and ions in organic as well as inorganic compounds. Obviously, the cyano group is involved in a complex and comprehensive chemistry in the ISM. Organic compounds possessing the cyano group are usually called nitriles. Several series of nitriles exist in the ISM. One example is the H(C≡C)n–C≡N series, where members with n in the range 0 to 5 have been identified (Snyder & Buhl 1971; Turner 1971; Avery et al. 1976; Broten et al. 1976, 1978; Kroto et al. 1978; Little et al. 1978; Winnewisser & Walmsley 1978; Bell et al. 1997). Another similar series includes the methyl group (CH3). Three examples of the CH3(C≡C)n–C≡N series with n = 0–2 have been found (Solomon et al. 1971; Broten et al. 1984; Snyder et al. 2006). Two other nitriles of relevance for the studied compound, namely, CnH2n+1C≡N, where n is 2 or 3, exist in space (Johnson et al. 1977; Belloche et al. 2009). This first study of the rotational spectrum of ethyl cyanoacetylene (C2H5C≡C–C≡N) was performed because this nitrile is chemically closely related to members of these series of nitriles. This fact alone suggests that the studied compound may be a component of the ISM. Consequently, it was thought worthwhile to synthesize C2H5C≡C–C≡N and study its rotational spectrum to obtain data for use in a potential detection of this compound anywhere in the ISM. It is not expected that C2H5C≡C–C≡N is a prominent interstellar, cometary, or atmospheric specie, but, hopefully, new and vastly improved radio astronomical observatories such as ALMA may be capable of detecting it using the spectral material we present here. This paper is organized in several sections and a conclusion. Section 2 presents some possible chemical pathways for the formation of the studied compound. Section 3 gives some details about the experimental set-up and the ethyl cyanoacetylene synthesis. Section 4 covers the ab initio calculations and their analysis. Section 5 presents the experimental results and the assignment of the microwave spectrum. Section 6 is dedicated to the experimental dipole moment determination.

2. Possible formation mechanisms for ethyl cyanoacetylene

There are no experimental data for the heat of formation of ethyl cyanoacetylene, but it could be thermodynamically more stable than both HC≡C–C≡N and CH3C≡C–C≡N. There are two reasons for this assumption. First, the heat of formation decrease of the CnH2n+1C≡N series with n = 0 to 3 is 135.14, 74.04, 51.46, and 31.2 kJ/mol. Secondly, in the analogous alkyne series CnH2n+1C≡CH with n = 0 to 2, the heat of formation decrease is 226.73, 185.4, and 165.2 kJ/mol (Nist web book accessed January 2013). Ethyl cyanoacetylene contains the saturated ethyl group (C2H5) and the unsaturated C≡C–C≡N part. The fact that several unsatured-satured molecules have been detected in the ISM including C2H5C≡N, n-C3H7C≡N, C2H5OC(O)H (Belloche et al. 2009) and the following methyl species CH3C≡CC≡N, CH3C≡CC≡CC≡N, CH3C≡N, CH3OC(O)H, CH3C(O)NH2 (Brown et al. 1975; Churchwell & Winnewisser 1975; Hollis et al. 2006) makes it likely that ethyl cyanoacetylene may be also present in this medium.

The formation of complex molecules (six or more atoms) in dense interstellar clouds may be available in gas phase from precursors that are formed on the grain surface (Vasyunin & Herbst 2013). The radical-radical association and the radical-neutral reactions are known to be efficient at low temperature in the gas phase because they are generally energy-barierless (Troe 2003; Klippenstein et al. 2006). Considering these kind of reactions, we suggest several chemical pathways for the formation of ethyl cyanoacetylene.

Very recent high-level ab initio and density functional theory (DFT) calculations may indicate that C2H5C≡C–C≡N and atomic hydrogen may be formed in a reaction between the precursor 1-butyne (CH3CH2C≡CH) and the C≡N radical (Jamal & Mebel 2013). The C≡N radical in the ISM has been observed for a long time (Solomon 1973; Allen & Knapp 1978) and has recently been proposed as tracer for the magnetic field characterization in several dense clouds (Hakobian & Crutcher 2011; Crutcher et al. 1999). It is worth noting that 1-butyne has so far not been identified in this medium, although it is listed as a potential interstellar compound (Woon & Herbst 2009) and its relative abundance upper limit compare to H2 in TMC-1 has been estimated to 3 × 10-9 (Irvine 1987). This could be explained by a probably quite small abundance but also by a low dipole moment of only 0.76D (Landsberg & Suenram 1983).

A second chemical pathway for the formation of C2H5C≡C–C≡N may be the gas phase radical-radical association reaction between C≡C–C≡N and the alkyl precursor C2H5. Only the C≡C–C≡N radical has been identified in the ISM to date (Guelin & Thaddeus 1977). C2H5 may be relatively abundant, but its small dipole moment (about 0.25 D (Rudic et al. 2004)) is not favorable for a potential detection. A third gas phase process with the same precursor may be the reaction between HC3N and C2H5. This kind of addition-elimination has been studied in theory (James & Ogawa 1965; James & MacCallum 1965) and a few experimental studies in the laboratory have been made (Getty et al. 1967), but it could lead to a simple addition on the triple bond to form an alkenyl radical.

At last, an alternative answer could be the reaction of cation and CH3C≡C–C≡N followed by a dissociative recombination of the generated cation C2H5C≡C–C≡NH+ to form C2H5C≡C–C≡N and H. is probably a key compound in the carbon chemistry of the ISM and has been proposed as one of the most abundant positive ions in dense clouds in several works (Opendak & Varshalovich 1986). Several experimental works have been performed in the gas phase on similar reactions as with CH4, HC≡N, CH3C≡N or HC≡CC≡N (Anicich 2003). For all these reactions the exit channel that corresponds to the addition process has been observed.

All these reaction paths include some hypothetical (because not detected) precursor species, but remain possible. The fact that some detected compounds similar to ethyl cyanoacetylene, bearing a saturated ethyl group and an unsaturated group, have a smaller dipole moment therefore suggests a possible detection of C2H5C≡C–C≡N if it is present in reasonable amounts.

3. Experimental

Ethyl cyanoacetylene (2-pentynenitrile) is usually synthesized by reaction of ClCN with 1-butynyl lithium (Van der Welle & Brandsma 1973; Brandsma & Verkruijsse 1981). ClCN is a very toxic compound, not easy to synthesize or use safely (Coleman et al. 1946). Consequently, we prepared ethyl cyanoacetylene by dehydratation of the corresponding amide in the same way as used by Moureu and Bongrand at the beginning of the 20th century to synthesize cyanoacetylene (Moureu & Bongrand 1920). Ethyl pent-2-ynoate was purchased from Alfa-Aesar and used without further purification. 2-Pentynamide was prepared as previously reported (Strubing et al. 2005).

In a 100 mL round-bottomed flask, 2-pentynamide (4.85 g, 50 mmol) was carefully mixed with sea sand (20 g) and phosphorus pentoxide (15 g). The flask was attached to a vacuum line equipped with two traps and evacuated. The flask was immersed in an oil bath, the first trap was immersed in a bath cooled at 0 °C and the second one in a bath cooled at −80 °C. The oil bath was gradually heated to 180 °C for about 2 h. High boiling impurities were trapped in the first trap and ethyl cyanoacetylene was selectively trapped in the second trap. At the end of the reaction, ethyl cyanoacetylene was transferred under vacuum to a cell equipped with a stopcock and the product was kept for months in a freezer (−20 °C) without any decomposition. Yield 72% (2.84 g, 3.6 mmol). 1H and 13C NMR data of 2-pentynamide and ethyl cyanoacetylene are as follows: 2-pentynamide: 1H NMR (CDCl3, 400 MHz, 25 °C) δ 1.16 (t, 3H, 3JHH = 7.5 Hz, CH3) ; 2.28 (q, 2H, 3JHH = 7.5 Hz, CH2) ; 5.9 and 6.4 (s, brd, 2H, NH2). 13C NMR (CDCl3, 100 MHz, 25 °C) δ 12.4 (q, 1JCH = 132.0 Hz, CH3), 12.8 (t, 1JCH = 129.8 Hz, CH2), 74.4 (s, C-CO), 90.1 (s, CC-CO), 155.7 (s, C=O). Ethyl cyanoacetylene: 1H NMR (CDCl3, 400 MHz, 25 °C) δ 1.22 (t, 3H, 3JHH = 7.5 Hz, CH3); 2.36 (q, 2H, 3JHH = 7.5 Hz, CH2). 13C NMR (CDCl3, 100 MHz, 25 °C) δ 11.9 (q, 1JCH = 132.3 Hz, CH3), 12.6 (t, 1JCH = 129.8 Hz, CH3), 54.6 (s, C-CN), 88.4 (s, CC-CN), 105.2 (s, CN).

The microwave spectrometer of the Oslo University used for this study has been described elsewhere (Møllendal et al. 2005, 2006). This spectrometer has a resolution of 0.5 MHz and measures the frequency of isolated transitions with an accuracy of 0.1 MHz. The frequency synthesizer is a 2–26.5 GHz 1730B Systron Donner model and the lock in amplifier control is a 0.5 Hz–120 kHz 5209 Perkin Elmer Instruments model. Several frequency multipliers were used to study the microwave spectrum of C2H5C≡C–C≡N between 13–116 GHz spectral range by Stark modulation spectroscopy. Double-resonance radio-frequency microwave experiments (RFMWDR), similar to those performed by Wodarczyk and Wilson (Wodarczyk & Wilson 1971), were employed to unambiguously assign several transitions using the equipment described elsewhere (Leonov et al. 2000) The radio frequency source was a Rohde & Schwarz SML01 signal generator operating in the 9 kHz-1.1 GHz spectral region. An EIN Model 503L amplifier provided 3 W linear amplification of the radio signals between 2 and 510 MHz. Mixing of the radio signal with the Stark modulation signal was provided using a Hewlett-Packard 10514 mixer. The pressure in the spectrometer cell was approximately 10 Pa and the temperature was maintained at room temperature, or at −30 °C, by cooling the 2 m Hewlett-Packard absorption cell with dry ice to enhance intensities.

4. Quantum-chemical calculations

Prediction of accurate spectroscopic constants greatly facilitates the assignment of complex rotational spectra such as that encountered for CH3CH2C≡C–C≡N. Fortunately, high-level quantum-chemical calculations are now capable of providing such parameters.

The present quantum-chemical calculations were performed employing the Gaussian 09 program package (Frisch et al. Gaussian09) running with the ABEL Linux cluster of the University of Oslo. Becke’s three-parameter hybrid functional (Becke 1988) employing the Lee, Yang, and Parr correlation functional (B3LYP; Lee et al. 1988) was used in the density functional theory calculations (DFT). Ab initio coupled-cluster calculations with singlet and doublet excitations (CCSD; Purvis & Bartlett 1982; Scuseria et al. 1988) were also undertaken. Peterson and Dunning’s correlation consistent cc-pVTZ basis set, (Peterson & Dunning 2002) which is of triple-ζ quality, was used in the calculations.

thumbnail Fig. 1

Model of ethyl cyanoacetylene (2-pentynenitrile) with atom numbering.

A model of ethyl cyanoacetylene with atom numbering is shown in Fig. 1. The geometry was first optimized at the B3LYP/cc-pVTZ level theory employing the default convergence criteria of Gaussian09. The molecule has CS symmetry plane with four out-of-plane hydrogen atoms (H2, H3, H4, H6 and H7). The B3LYP structure is shown in Table 1. The B3LYP dipole moment and its components along the principal inertial axes, the vibrational frequencies, Watson’s S-reduction quartic and sextic centrifugal distortion constants (Watson 1977), the vibration-rotation constants (the α’s) (Gordy & Cook 1984), and the nuclear quadrupole coupling constants of the 14N atom were then calculated. In these calculations, the B3LYP structure was held fixed in the principal inertial axis coordinate system to obtain correct centrifugal distortion and α-constants, as pointed out by McKean et al. (McKean et al. 2008). The dipole moment and the nuclear quadrupole coupling constants are listed in Table 2, the theoretical fundamental vibrational frequencies in Table 3, the α’s in Table 4, and the centrifugal distortion constants in Table 5. Finally, the geometry was optimized at the very high CCSD/cc-pVTZ level of theory. The resulting structure is listed in Table 1. The dipole moment and the 14N quadrupole coupling constants are given in Table 2. It was not possible to calculate vibrational properties at this level of theory with our present computational resources. Interestingly, the bond lengths (Table 1) are very similar at both theory levels except for two of them, namely, the C5-C8 and the C9-C10 bond lengths. These B3LYP bonds are shorter by 1.15 and 1.74 pm, respectively. The angles and dihedral angles agree well. The total dipole moments are μTOT = 5.41 D (B3LYP), and μTOT = 5.59 D (CCSD) (Table 2).

Table 1

Theoritical structures, principal moments of inertia, and rotational constants.

5. Microwave spectrum and assignment

The CCSD calculations (Table 2) predict a large dipole moment for C2H5C≡C–C≡N with a component of 5.55 D along the a-principal inertia axis, and a much smaller component of 0.69 D along the b-axis. The molecule is almost a completely prolate symmetrical top because of Ray’s asymmetry parameter (Ray 1932) κ ≈  −0.994. The spectrum was therefore predicted to be dominated by pile-ups of a-type R-branch transitions of ground- and vibrationally excited states separated by almost the exact sum of the B and C rotational constants.

The pile-ups were expected to have a very complex fine-structure, especially for high values of the J quantum number, because there are six transitions with fundamental frequencies below 500 cm-1 (Table 3) and each of the corresponding excited states will contribute their own spectra to each pile-up, making them very crowded. At low values of J, most of the K-1 lines will coalesce into one big, unresolved line, but at high values of J, centrifugal distortion will split the K-1 lines, allowing individual states to be assigned. This too adds to the complexity of the spectrum.

Table 2

Theoritical dipole moments and quadrupole coupling constants.

Table 3

Fundamental vibrational frequencies (cm-1).

Table 4

The B3LYP/cc-pVTZ vibro-rot alpha matrix (MHz).

Table 5

B3LYP/cc-pVTZ centrifugal distortion constants.

thumbnail Fig. 2

Portion of the J = 33 ← 32 transition of the rotational spectrum of C2H5C≡C–C≡N taken at a Stark field of about 150 V/cm. The values above several of the absorption peaks refer to the K-1 pseudo-quantum number. It was not possible to definitely assign values of K-1 higher than 15 because of overlapping transitions (extreme right of the picture). The most intense line to the extreme left consists of the unresolved K-1 = 5 and 6 transitions.

These predictions turned out to be true. For high values of J, a J+1 ← J pile-up covers a spectral region of several hundred MHz. A portion of one such pile-up involving the J = 33 ← 32 transition, is shown in Fig. 2. Ground-state transitions overlapping with vibrationally excited state lines occur frequently and severely complicated the assignment of this spectrum. The first unambiguous assignments were achieved in RFMWDR experiments performed on pairs of lines with the same K-1 pseudo-quantum number using the theoretical rotational and centrifugal distortion constants to predict their approximate frequencies. The Stark effect was also useful for the assignments of several transitions. The assignments were then gradually extended to include more K-1-transitions and transitions with increasingly higher values of J.

Sørensen’s program ROTFIT (Sørensen 1967) was used for a least-squares fit of the lines employing Watson’s S-reduction and Ir-representation (Watson 1977). Sharp and well-isolated transitions were assigned an uncertainty of 0.10 MHz, whereas larger uncertainties were used for other transitions. Because overlapping of transitions occurs very frequently, only well-isolated lines were included in the fit. Ultimately, 342 aR-transitions of the ground vibrational state (Table 6) were selected to obtain the best possible spectroscopic constants and a root-mean-square deviation (rms) similar to the experimental uncertainty of ±0.1 MHz. Values of the J quantum number between 3 and 44, and K-1 between 0 and 15 (Table 6) were employed. Comparatively few transitions with K-1 = 0, 1, and 2 were included in the fit because they frequently overlap with other transitions, or because they were not fully Stark-modulated and therefore could not be measured accurately. Attempts to assign b-type lines failed, presumably because μb is as small as 0.659(3) D (see below), producing insufficient intensities for secure assignments. It was not possible to derive the quadrupole coupling constants of 14N, because the corresponding splittings of the aR-lines are small and not resolved. This is in accord with predictions from program MB09 (Marstokk & Møllendal 1969) using the theoretical nuclear quadrupole coupling constants shown in Table 2.

In the fitting of the aR-lines, only the rotational constants and the centrifugal distortion constants DJ, DJK, HJ, HJK, and DKJ were employed, with the remaining centrifugal distortion constants preset at zero. This was done because the compound is practically a symmetrical top (κ ≈  −0.9942; Table 6). The centrifugal distortion constants excluded from the fit will therefore play an insignificant role. The resulting spectroscopic constants are shown in Table 7. This table also includes their theoretical counterparts. Excellent agreement exists between the experimental and CCSD rotational constants. The experimental quartic centrifugal distortion constants are in satisfactory agreement with their B3LYP counterparts, whereas the sextic B3LYP centrifugal distortion constants disagree with their experimental equivalents. It is seen from this table that the A rotational constant is poorly determined. The reason for this is that only aR-lines were assigned for this very prolate compound. Nevertheless, the spectroscopic constants shown in this table should be able to predict the frequencies of aR-transitions in spectral regions not covered by us with a very high degree of precision, because the A rotational constant influences the predictions to a minor degree.

Table 6

Rotational spectrum of C2H5C≡C–C≡N.

Attempts to assign excited states were also made. These attempts met with some success, but we did not obtain results that warrant publication because of the very crowded nature of the spectrum.

6. Dipole moment

The dipole moment was determined by a least-squares fitting of the second-order Stark coefficient shown in Table 8. The weight of each Stark coefficient was taken to be the inverse square of its standard deviation, which is also shown in the same table. The theoretical values of the second-order Stark coefficients were calculated as described by Golden and Wilson (Golden & Wilson 1948) using program MB04 (Marstokk & Møllendal 1969). The experimental dipole moment components are μa = 5.713(28), μb = 0.659(3), μc = 0.0 (preset) and μTOT = 5.751(28) Debye, where the uncertainties are 1 standard deviation. The dipole moment along the c-principal inertial axis, μc, is exactly zero because C2H5C≡C–C≡N has a symmetry plane. These experimental values agree well with the calculated dipole moments at the B3LYP/cc-pVTZ and CCSD/cc-pVTZ levels of theory (Table 2).

7. Conclusion

The microwave spectrum of the ground-vibrational state of ethyl cyanoacetylene was investigated in the 13–116 GHz range and 342 transitions with a maximum J = 44 and maximum K-1 = 15 were assigned and the experimental dipole moment was determined. The spectroscopic constants obtained from the least-squares fit should be capable of predicting very accurate frequencies of transitions that do not appear in the investigated spectral range. Hopefully, this spectral analysis of C2H5C≡C–C≡N will allow its detection in the ISM provided it is present in a suitable concentration.

Table 7

Spectroscopic constants of C2H5C≡C–C≡N.

Table 8

Spectroscopic constants of Stark coefficients and dipole moment of C2H5C≡C–C≡N.

Acknowledgments

We are grateful to Anne Horn for her skillful assistance. S.C. and J.-C.G. acknowledge the “Programme de Physique et Chimie du Milieu Interstellaire” and the “Programme National de Planétologie” (PCMI and PNP INSU-CNRS) and J.-C.G. acknowledge the “Centre Nationale d’Études Spatiales” (CNES) for financial support. This work has been supported by the Research Council of Norway through a Centre of Excellence Grant (Grant No. 179568/V30). It has also received support from the Norwegian Supercomputing Program (NOTUR) through a grant of computer time (Grant No. NN4654K).

References

  1. Allen, M., & Knapp, G. R. 1978, ApJ, 225, 843 [NASA ADS] [CrossRef] [Google Scholar]
  2. Anicich, V. G. 2003, JPL-Publication [Google Scholar]
  3. Avery, L. W., Broten, N. W., Macleod, J. M., Oka, T., & Kroto, H. W. 1976, ApJ, 205, L173 [NASA ADS] [CrossRef] [Google Scholar]
  4. Becke, A. D. 1988, Phys. Rev. A, 38, 3098 [Google Scholar]
  5. Bell, M. B., Feldman, P. A., Travers, M. J., et al. 1997, ApJ, 483, L61 [NASA ADS] [CrossRef] [Google Scholar]
  6. Belloche, A., Garrod, R. T., Muller, H. S. P., et al. 2009, A&A, 499, 215 [NASA ADS] [CrossRef] [EDP Sciences] [Google Scholar]
  7. Brandsma, L., & Verkruijsse, H. D. 1981, Studies in Organic Chemistry, Synthesis of acetylenes, allenes, and cumulenes: a laboratory manual (Amsterdam, New York: Elsevier Scientific Pub. Co.), 8, 62 [Google Scholar]
  8. Broten, N. W., Macleod, J. M., Oka, T., et al. 1976, ApJ, 209, L143 [NASA ADS] [CrossRef] [Google Scholar]
  9. Broten, N. W., Oka, T., Avery, L. W., MacLeod, J. M., & Kroto, H. W. 1978, ApJ, 223, L105 [NASA ADS] [CrossRef] [Google Scholar]
  10. Broten, N. W., Macleod, J. M., Avery, L. W., et al. 1984, ApJ, 276, L25 [NASA ADS] [CrossRef] [PubMed] [Google Scholar]
  11. Brown, R. D., Crofts, J. G., Godfrey, P. D., et al. 1975, ApJ, 197, L29 [NASA ADS] [CrossRef] [Google Scholar]
  12. Churchwell, E., & Winnewisser, G. 1975, A&A, 45, 229 [NASA ADS] [Google Scholar]
  13. Coleman, G. H., Leeper, R. W., & Schulze, C. C. 1946, Inorg. Synth., 2, 90 [CrossRef] [Google Scholar]
  14. Crutcher, R., Troland, T., Lazareff, B., Paubert, G., & Kazes, I. 1999, ApJ, 514, L121 [NASA ADS] [CrossRef] [Google Scholar]
  15. Frisch, M. J., Trucks, G. W., Schlegel, H. B., et al. 2009, Gaussian09 (Wallingford, CT: Gaussian, INC.) [Google Scholar]
  16. Getty, R. R., Kerr, J. A., & Trotman-Dickenson, A. F. 1967, J. Chem. Soc. A, , 979 [CrossRef] [Google Scholar]
  17. Golden, S., & Wilson, E. B. 1948, J. Chem. Phys., 16, 669 [NASA ADS] [CrossRef] [Google Scholar]
  18. Gordy, W., & Cook, R. L. 1984, Microwave Molecular Spectra, ed. J. W. Sons, XVII (New York) [Google Scholar]
  19. Guelin, M., & Thaddeus, P. 1977, ApJ, 212, L81 [NASA ADS] [CrossRef] [Google Scholar]
  20. Hakobian, N. S., & Crutcher, R. M. 2011, ApJ, 733 [Google Scholar]
  21. Hollis, J. M., Lovas, F. J., Remijan, A. J., et al. 2006, ApJ, 643, L25 [Google Scholar]
  22. Irvine, W. M. 1987, in Astrochemistry, eds. M. S. Vardya, & S. P. Tarafdar, IAU Symp., 120, 245 [Google Scholar]
  23. Jamal, A., & Mebel, A. 2013, J. Phys. Chem. A, 117, 741 [CrossRef] [Google Scholar]
  24. James, D. G. L., & MacCallum, D. 1965, Can. J. Chem., 43, 633 [CrossRef] [Google Scholar]
  25. James, D. G. L., & Ogawa, T. 1965, Can. J. Chem., 43, 640 [CrossRef] [Google Scholar]
  26. Johnson, D. R., Lovas, F. J., Gottlieb, C. A., et al. 1977, ApJ, 218, 370 [NASA ADS] [CrossRef] [Google Scholar]
  27. Klippenstein, S. J., Georgievskii, Y., & Harding, L. B. 2006, Phys. Chem. Chem. Phys., 8, 1133 [CrossRef] [Google Scholar]
  28. Kroto, H. W., Kirby, C., Walton, D. R. M., et al. 1978, ApJ, 219, L133 [NASA ADS] [CrossRef] [Google Scholar]
  29. Landsberg, B., & Suenram, R. 1983, J. Mol. Spectrosc., 98, 210 [Google Scholar]
  30. Lee, C. T., Yang, W. T., & Parr, R. G. 1988, Phys. Rev. B, 37, 785 [Google Scholar]
  31. Leonov, A., Marstokk, K.-M., de Meijere, A., & Møllendal, H. 2000, J. Phys. Chem. A, 104, 4421 [CrossRef] [Google Scholar]
  32. Little, L. T., Macdonald, G. H., Riley, P. W., & Matheson, D. N. 1978, MNRAS, 183, 45 [Google Scholar]
  33. Marstokk, K.-M., & Møllendal, H. 1969, J. Mol. Spectr., 4, 470 [NASA ADS] [CrossRef] [Google Scholar]
  34. McKean, D., Craig, N., & Law, M. 2008, J. Phys. Chem. A, 112, 6760 [CrossRef] [Google Scholar]
  35. Møllendal, H., Leonov, A., & de Meijere, A. 2005, J. Phys. Chem. A, 109, 6344 [CrossRef] [Google Scholar]
  36. Møllendal, H., Cole, G. C., & Guillemin, J. C. 2006, J. Phys. Chem. A, 110, 921 [CrossRef] [Google Scholar]
  37. Moureu, C., & Bongrand, J. C. 1920, Ann. Chim. (Fr), 14, 47 [Google Scholar]
  38. Nist web book, w. s. accessed January 2013, http://webbook.nist.gov/chemistry/ [Google Scholar]
  39. Opendak, M. G., & Varshalovich, D. A. 1986, Soviet Astron., 30, 274 [NASA ADS] [Google Scholar]
  40. Peterson, K. A., & Dunning, T. H. 2002, J. Chem. Phys., 117, 10548 [NASA ADS] [CrossRef] [Google Scholar]
  41. Purvis, G. D., & Bartlett, R. J. 1982, J. Chem. Phys., 76, 1910 [NASA ADS] [CrossRef] [Google Scholar]
  42. Ray, B. S. 1932, Z. Phys., 78, 74 [Google Scholar]
  43. Rudic, S., Murray, C., Harvey, J. N., & Orr-Ewing, A. J. 2004, J. Chem. Phys., 120, 186 [NASA ADS] [CrossRef] [Google Scholar]
  44. Scuseria, G. E., Janssen, C. L., & Schaefer, H. F. 1988, J. Chem. Phys., 89, 7382 [NASA ADS] [CrossRef] [Google Scholar]
  45. Snyder, L. E., & Buhl, D. 1971, ApJ, 163, L47 [NASA ADS] [CrossRef] [Google Scholar]
  46. Snyder, L. E., Hollis, J. M., Jewell, P. R., Lovas, F. J., & Remijan, A. 2006, ApJ, 647, 412, part 1 [NASA ADS] [CrossRef] [Google Scholar]
  47. Solomon, P. 1973, Phys. Today, 26, 32 [CrossRef] [Google Scholar]
  48. Solomon, P. M., Jefferts, K. B., Penzias, A. A., & Wilson, R. W. 1971, ApJ, 168, L107 [NASA ADS] [CrossRef] [Google Scholar]
  49. Sørensen, G. O. 1967, J. Mol. Spectr., 22, 325 [NASA ADS] [CrossRef] [Google Scholar]
  50. Strubing, D., Neumann, H., Klaus, S., Hubner, S., & Beller, M. 2005, Tetrahedron, 61, 11333 [CrossRef] [Google Scholar]
  51. Troe, J. 2003, Chem. Rev., 103, 4565 [CrossRef] [Google Scholar]
  52. Turner, B. E. 1971, ApJ, 163, L35 [NASA ADS] [CrossRef] [Google Scholar]
  53. Van der Welle, R. A., & Brandsma, L. 1973, Rec. Trav. Chim. Pays-Bas, 92, 667 [CrossRef] [Google Scholar]
  54. Vasyunin, A. I., & Herbst, E. 2013, ApJ, 769, 34 [Google Scholar]
  55. Watson, J. 1977, Vibrational Spectra and Structure., ed. J. Durig (Amsterdam: Elsevier), 8, 1 [Google Scholar]
  56. Winnewisser, G., & Walmsley, C. M. 1978, A&A, 70, L37 [NASA ADS] [Google Scholar]
  57. Wodarczyk, F., & Wilson, E. B. 1971, J. Mol. Spectr., 37, 445 [NASA ADS] [CrossRef] [Google Scholar]
  58. Woon, D. E., & Herbst, E. 2009, ApJS, 185, 273 [NASA ADS] [CrossRef] [Google Scholar]

All Tables

Table 1

Theoritical structures, principal moments of inertia, and rotational constants.

In the text
Table 2

Theoritical dipole moments and quadrupole coupling constants.

In the text
Table 3

Fundamental vibrational frequencies (cm-1).

In the text
Table 4

The B3LYP/cc-pVTZ vibro-rot alpha matrix (MHz).

In the text
Table 5

B3LYP/cc-pVTZ centrifugal distortion constants.

In the text
Table 6

Rotational spectrum of C2H5C≡C–C≡N.

In the text
Table 7

Spectroscopic constants of C2H5C≡C–C≡N.

In the text
Table 8

Spectroscopic constants of Stark coefficients and dipole moment of C2H5C≡C–C≡N.

In the text

All Figures

thumbnail Fig. 1

Model of ethyl cyanoacetylene (2-pentynenitrile) with atom numbering.
In the text
thumbnail Fig. 2

Portion of the J = 33 ← 32 transition of the rotational spectrum of C2H5C≡C–C≡N taken at a Stark field of about 150 V/cm. The values above several of the absorption peaks refer to the K-1 pseudo-quantum number. It was not possible to definitely assign values of K-1 higher than 15 because of overlapping transitions (extreme right of the picture). The most intense line to the extreme left consists of the unresolved K-1 = 5 and 6 transitions.
In the text

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.