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15NH3 is the object of extensive investigation due to the central role of ammonia in astronomical sciences and to the complexity of modeling its interacting vibrationally excited states. Of major interest in astrochemistry is the determination of the 14N/15N ratio in space, characterized by unexpected variability among different solar system objects and reservoirs. Recently, the spectroscopic analysis of ground and v2 = 1 a, s states of 15NH3 has been completed at experimental accuracy. Here, the characterization of the a, s inversion symmetry levels of v2 = 1, 2 and v4 = 1 states is presented. New spectra of 15NH3 have been recorded from 325 to 2000 cm−1 at a resolution ranging from 0.00096 cm−1 to 0.003 cm−1, using the Canadian Light Source synchrotron at CLS. 7518 transitions covering nine bands, ν2, 2ν2, ν4, 2ν2 ← ν2, ν4 ← ν2, 2ν2 ↔ ν4 and the inversion-rotation transitions in the excited states, have been fitted simultaneously. The effective Hamiltonian adopted includes all symmetry allowed interactions between and within the studied excited states, according to the most recent results on ammonia. The transitions have been reproduced at experimental accuracy using 185 spectroscopic parameters, determined with high precision. The leading diagonal parameters, Gv, B, C, D's, compare well with those of 14NH3. The wavenumbers of the assigned transitions are compared with their theoretically predicted values. An improved set of ground state parameters is also derived. These results noticeably improve the wavenumber line list in the high-resolution transmission molecular absorption (HITRAN) database. [ABSTRACT FROM AUTHOR]

Infrared and Raman spectra of mono 13C fully deuterated acetylene, 13C12CD2, have been recorded and analysed to obtain detailed information on the C--D stretching fundamentals and associated combination, overtone, and hot bands. Infrared spectra were recorded at an instrumental resolution ranging between 0.006 and 0.01 cm-1 in the region 1800-7800 cm-1. Sixty new bands involving the ν1 and ν3 C--D stretching modes also associated with the ν4 and ν5 bending vibrations have been observed and analysed. In total, 5881 transitions have been assigned in the investigated spectral region. In addition, the Q branch of the ν1 fundamental was recorded using inverse Raman spectroscopy, with an instrumental resolution of about 0.003 cm-1. The transitions relative to each stretching mode, i.e., the fundamental band, its first overtone, and associated hot and combination bands involving bending states with υ4 + υ5 up to 2 were fitted simultaneously. The usual Hamiltonian appropriate to a linear molecule, including vibration and rotation l-type and the Darling-Dennison interaction between υ4 = 2 and υ5 = 2 levels associated with the stretching states, was adopted for the analysis. The standard deviation for each global fit is ≤0.0004 cm-1, of the same order of magnitude of the measurement precision. Slightly improved parameters for the bending and the ν2 manifold have been also determined. Precise values of spectroscopic parameters deperturbed from the resonance interactions have been obtained. They provide quantitative information on the anharmonic character of the potential energy surface, which can be useful, in addition to those reported in the literature, for the determination of a general anharmonic force field for the molecule. Finally, the obtained values of the Darling-Dennison constants can be valuable for understanding energy flows between independent vibrations. [ABSTRACT FROM AUTHOR]

The high-resolution infrared spectrum of monodeuterated diacetylene has been recorded in the 450-1100 cm-1 spectral region by Fourier transform infrared spectroscopy. Seven new bands have been identified: the ν3 fundamental (C-C stretch), and the ν8 + ν9, ν7 + ν8, 2ν7, 2ν8, ν8 + ν9 - ν9, and ν6 + ν9 - ν9 combination, overtone, and hot bands. The assigned transitions, together with those previously reported for the fundamental bands [F. Tamassia, L. Bizzocchi, C. Degli Esposti, L. Dore, M. Di Lauro, L. Fusina, M. Villa, and E. Canè, Astron. Astrophys. 549, A38 (2013)], form a comprehensive data set which comprises more than 2500 ro-vibrational transitions, and involves all singly and most doubly excited vibrational states of DC4H lying below 1000 cm-1. Rotational and vibrational l-type resonance effects among the sub-levels of excited bending states were considered in the analysis, which also included a careful treatment of the various anharmonic interactions coupling many vibrational states lying above 600 cm-1. Reliable and unambiguous spectroscopic parameters were obtained for each investigated state, including the rotational and centrifugal distortion constants Bv and Dv, the l-type doubling parameter qt, the anharmonicity constants xL(89), xL(69), and the vibrational l-type terms r89, r69 for the v8 = v9 = 1 and v6 = v9 = 1 bend-bend combination states. [ABSTRACT FROM AUTHOR]

We present the study of deuteration of cyanoacetylene (HC3N) towards a sample of 28 high-mass star-forming cores divided into different evolutionary stages, from starless to evolved protostellar cores. We report for the first time the detection of DC3N towards 15 high-mass cores. The abundance ratios of DC3N with respect HC3N range in the interval 0.003–0.022, lower than those found in low-mas protostars and dark clouds. No significant trend with the evolutionary stage, or with the kinetic temperature of the region, has been found. We compare the level of deuteration of HC3N with those of other molecules towards the same sample, finding weak correlation with species formed only or predominantly in gas phase (N2H+ and HNC, respectively), and no correlation with species formed only or predominantly on dust grains (CH3OH and NH3, respectively). We also present a single-dish map of DC3N towards the protocluster IRAS 05358+3543, which shows that DC3N traces an extended envelope (∼0.37 pc) and peaks towards two cold condensations separated from the positions of the protostars and the dust continuum. The observations presented in this work suggest that deuteration of HC3N is produced in the gas of the cold outer parts of massive star-forming clumps, giving us an estimate of the deuteration factor prior to the formation of denser gas. [ABSTRACT FROM AUTHOR]

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)]. [ABSTRACT FROM AUTHOR]

The rotational spectrum of the triatomic free radical SiOH in its X 2A′ ground electronic state has been observed in a supersonic molecular beam by Fourier transform microwave spectroscopy. The fundamental (10,1→00,0) transition has been detected for normal SiOH and for three rare isotopic species: 30SiOH, Si18OH, and SiOD. The same transition has also been observed in two of three excited vibrational states, v2 and v3, for the most abundant species. Precise spectroscopic constants, including those that describe the effective spin doubling and hydrogen hyperfine structure, have been derived for each isotopic species or vibrational state. To complement the laboratory work, theoretical calculations of the structure, dipole moment, and energies of the X 2A′ and low-lying 1 2A″ states have also been undertaken at the coupled cluster level of theory. In agreement with theoretical predictions, we conclude from the hyperfine constants that SiOH is a best described as a π-type radical, with the unpaired electron localized on a p orbital on the silicon atom. Assuming a bond angle of 118.5°, the Si–O bond length is 1.647(2) Å and the O–H bond length is 0.969(4) Å. [ABSTRACT FROM AUTHOR]

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 e/f 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. [ABSTRACT FROM AUTHOR]

In 12C13CH2 129 vibrational term values up to 10 000 cm-1 are merged, about 60% of which are newly reported. They are fitted using an effective Hamiltonian with a standard deviation of 0.22 cm-1. The vibrational assignments and vibrational constants are listed and discussed. The energy pattern is found to be very similar to the one in 12C2H2 with additional anharmonic resonances arising from the lack of u/g character in the asymmetric isotopolog. [ABSTRACT FROM AUTHOR]

Context. Isotopic fractionation in dense molecular cores has been suggested as a possible origin of large 14N/15N ratio variations in solar system materials. While chemical models can explain some observed variations with different fractionation patterns for molecules with –NH or –CN functional groups, they fail to reproduce the observed ratios in diazenylium (N2H+). Aims. Observations of doubly 15N-substituted species could provide important constraints and insights for theoretical chemical models of isotopic fractionation. However, spectroscopic data are very scarce. Methods. The rotational spectra of the fully 15N-substituted isopologues of the diazenylium ion, 15N2H+ and 15N2D+, have been investigated in the laboratory well into the THz region by using a source-modulation microwave spectrometer equipped with a negative glow discharge cell. An extended chemical reaction network has been used to estimate what ranges of 15N fractionation in doubly 15N-substituted species could be expected in the interstellar medium (ISM). Results. For each isotopologue of the H- and D-containing pair, nine rotational transitions were accurately measured in the frequency region 88 GHz–1.2 THz. The analysis of the spectrum provided very precise rest frequencies at millimeter and sub-millimeter wavelengths, useful for the radioastronomical identification of the rotational lines of 15N2H+ and 15N2D+ in the ISM. [ABSTRACT FROM AUTHOR]