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The rotational spectra of the butadiyne anion C 4 H Ϫ and the octatetrayne anion C 8 H Ϫ have been detected in the laboratory. Precise spectroscopic constants for these closed-shell molecules have been obtained, which enable their rotational spectra to be calculated to high accuracy throughout the radio band. Deep astronomical searches can now be undertaken in essentially any molecular source, including TMC-1 and IRC ϩ10216, where the negative ion C 6 H Ϫ has recently been detected. The large dipole moments and high binding energies of both anions make them good candidates for astronomical detection.We recently detected the radio spectrum of the negative ion C 6 H Ϫ in the laboratory and showed that this suprisingly large carbon chain anion is the carrier of the unidentified harmonic sequence of molecular lines B1377 observed by Kawaguchi et al. (1995) in the circumstellar shell of the carbon star IRC ϩ10216 (McCarthy et al. 2006). The radio spectra of other molecular anions should now be detectable in the laboratory and in space, especially linear closed-shell carbon chains similar in structure to C 6 H Ϫ . Here we report laboratory detection of the next shorter and the next longer members of the series, the butadiyne anion C 4 H Ϫ and the octatetrayne anion C 8 H Ϫ . Precise transition frequencies over most of the radio band are now available for astronomical searches for these anions.Like C 6 H Ϫ , the C 4 H Ϫ anion has been observed in both the millimeter-wave band with a free space (FS) spectrometer (Gottlieb et al. 2003) and the centimeter-wave band with a Fourier transform microwave (FTM) spectrometer (McCarthy et al. 2000). The longer anion C 8 H Ϫ has only been detected with the highly sensitive FTM instrument, since its rotational lines are fairly weak. Seventeen rotational transitions between 9 and 363 GHz of C 4 H Ϫ and nine successive rotational transitions between 9 and 19 GHz of C 8 H Ϫ have been measured to an accuracy approaching 1 part in 10 7 (see Tables 1 and 2).In the FS spectrometer, C 4 H Ϫ was produced by a DC glow discharge through a flowing mixture of argon (15%) and acetylene (85%) at a total pressure of ≤10 mtorr with the discharge cell walls cooled to 100 K. As with C 6 H Ϫ , the optimum discharge current (∼150 mA) was substantially lower than that which produces the most intense lines of the neutral radical (∼400 mA). At this lower current, lines of C 4 H Ϫ were only about 8 times weaker than those of either fine-structure component of C 4 H; hyperfine structure of C 4 H collapses at high J and is not resolved at millimeter wavelengths, but spin-doubling does not collapse and is resolved. Taking the different partition functions and dipole moments into account, the abundance of the anion is found to be ∼0.14% that of the neutral. The absorption J p 37 R 36 line of C 4 H Ϫ is shown in Figure 1; a signal-to-noise ratio of ∼75 was obtained in only 25 minutes of integration, allowing line frequencies to be measured to 10-20 kHz.In the FTM spectrometer, the anions were produced under disc...

All known vibration-rotation absorption lines of 13CH12CH accessing levels up to 6750 cm-1 were gathered from the literature. They were fitted simultaneously to J-dependent Hamiltonian matrices exploiting the well known vibrational polyad or cluster block diagonalization, in terms of the pseudo-quantum-numbers Ns=v1+v2+v3 and Nr=5v1+3v2+5v3+v4+v5, and accounting also for l parity and ef symmetry properties. The anharmonic interaction coupling terms known to occur from a pure vibrational fit in this acetylene isotopologue [Robert et al., J. Chem. Phys. 123, 174302 (2005)] were included in the model. A total of 12 703 transitions accessing 158 different (v1v2v3v4v5,l4l5) vibrational states was fitted with a dimensionless standard deviation of 0.99, leading to the determination of 216 vibration-rotation parameters. The experimental data included very weak vibration-rotation transitions accessing 18 previously unreported states, some of them forming Q branches with very irregular patterns.

HC 3 N is an ubiquitous molecule in interstellar environments, from external galaxies, to Galactic interstellar clouds, star forming regions, and planetary atmospheres. Observations of its rotational and vibrational transitions provide important information on the physical and chemical structure of the above environments. We present the most complete global analysis of the spectroscopic data of HC 3 N. We have recorded the high-resolution infrared spectrum from 450 to 1350 cm −1 , a region dominated by the intense ν 5 and ν 6 fundamental bands, located at 660 and 500 cm −1 , respectively, and their associated hot bands. Pure

The electric quadrupole fundamental (v=1←0) band of molecular deuterium around 3 μm is accessed by cavity ring-down spectroscopy using a difference-frequency-generation source linked to the Cs-clock primary standard via an optical frequency comb synthesizer. An absolute determination of the line position and strength is reported for the first two transitions (J=2←0 and J=3←1) of the S branch. An accuracy of 6×10(-8) is achieved for the line-center frequencies, which improves by a factor 20 previous experimental results [A. R. W. McKellar and T. Oka, Can. J. Phys. 56, 1315 (1978)]. The line strength values, measured with 1% accuracy, are used to retrieve the quadrupole moment matrix elements which are found in good agreement with previous theoretical calculations [A. Birnbaum and J. D. Poll, J. Atmos. Sci. 26, 943 (1969); J. L. Hunt, J. D. Poll, and L. Wolniewicz, Can. J. Phys. 62, 1719 (1984)].