The v2 = 1, 2 and v4 = 1 bending states of 15NH3 and their analysis at experimental accuracy.

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.

High resolution infrared and Raman spectra of (13)C(12)CD2: The CD stretching fundamentals and associated combination and hot bands.

Infrared and Raman spectra of mono (13)C fully deuterated acetylene, (13)C(12)CD2, 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.

The high-resolution infrared spectrum of DC4H from 450 to 1100 cm-1: overtone, combination, and hot bands.

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.

Absolute measurement of the S(0) and S(1) lines in the electric quadrupole fundamental band of D(2) around 3µm.

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)].

Vibration-rotation energy pattern in acetylene: (13)CH(12)CH up to 10 120 cm(-1).

All 18,219 vibration-rotation absorption lines of (13)CH(12)CH published in the literature, accessing substates up to 9400 cm(-1) and including some newly assigned, were simultaneously fitted to J-dependent Hamiltonian matrices exploiting the well-known vibrational polyad or cluster block-diagonalization, in terms of the pseudo quantum numbers N(s) = v(1) + v(2) + v(3) and N(r) = 5v(1) + 3v(2) + 5v(3) + v(4) + v(5), also accounting for k = l(4) + l(5) parity and e/f symmetry properties. Some 1761 of these lines were excluded from the fit, corresponding either to blended lines, for about 30% of them, or probably to lines perturbed by Coriolis for the remaining ones. The dimensionless standard deviation of the fit is 1.10, and 317 vibration-rotation parameters are determined. These results significantly extend those of a previous report considering levels below only 6750 cm(-1) [Fayt, A.; et al. J. Chem. Phys. 2007, 126, 114303]. Unexpected problems are reported when inserting in the global fit the information available on higher-energy polyads, extending from 9300 to 10 120 cm(-1). They are tentatively interpreted as resulting from a combination of the relative evolution of the two effective bending frequencies and long-range interpolyad low-order anharmonic resonances. The complete database, made of 18,865 vibration-rotation lines accessing levels up to 10 120 cm(-1), is made available as Supporting Information.

A laboratory and theoretical study of silicon hydroxide SiOH.

The rotational spectrum of the triatomic free radical SiOH in its X (2)A(') ground electronic state has been observed in a supersonic molecular beam by Fourier transform microwave spectroscopy. The fundamental (1(0,1)-->0(0,0)) transition has been detected for normal SiOH and for three rare isotopic species: (30)SiOH, Si(18)OH, and SiOD. The same transition has also been observed in two of three excited vibrational states, v(2) and v(3), 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 (2)A(') and low-lying 1 (2)A(") 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 pi-type radical, with the unpaired electron localized on a p orbital on the silicon atom. Assuming a bond angle of 118.5 degrees , the Si-O bond length is 1.647(2) A and the O-H bond length is 0.969(4) A.

Vibration-rotation energy pattern in acetylene: 13CH12CH up to 6750 cm-1.

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.

The vibrational energy pattern in acetylene VII: (12)C(13)CH2.

In (12)C(13)CH(2) 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 (12)C2H2 with additional anharmonic resonances arising from the lack of u/g character in the asymmetric isotopolog.

A Study of the (2-0) Overtone Bands of the FO, BrO, and IO Free Radicals by Laser Magnetic Resonance.

The (2-0) overtone bands of the FO, BrO, and IO free radicals in their ground electronic state X(2)Pi(3/2) have been detected by laser magnetic resonance. The data obtained from this work have been fitted together with data from previous work. A set of molecular parameters, including vibrational, rotational, centrifugal distortion, spin-orbit, lambda-doubling, hyperfine, and Zeeman terms, has been determined for each molecule. Copyright 2001 Academic Press.

The Coriolis Interaction between the v2 = 1 and v3 = 2 States of Nitrosyl Bromide: Anomalous Quadrupole Patterns and Interstate Transitions in the Millimeter-Wave Spectrum.

The millimeter-wave rotational spectra of 79BrNO and 81BrNO in the v2 = 1 and v3 = 2 vibrational states have been reinvestigated. Measurements of the rotational spectrum in the region of maximum c-type Coriolis interaction between the two states allowed the previous analysis to be extended to account for some uncommon effects. For the most perturbed transitions the nuclear quadrupole hyperfine structure arises from coupling of not only the bromine nucleus, but also the nitrogen nucleus with the rotational angular momentum. These effects were satisfactorily fitted with a Hamiltonian describing Coriolis coupling in a molecule with two quadrupolar nuclei. The successful analysis of pure rotational transitions then allowed accurate prediction of rovibrational transitions, six of which were measured for 79BrNO and four for 81BrNO. Copyright 1998 Academic Press.

Diode Laser and FTIR Spectroscopy of BrCN Isotopomers in the Region of the nu3 Band.

The nu3 fundamental band (C-N stretch) and four associated hot bands (01(1)1-01(1)0, 10(0)1-10(0)0, 02(0)1-02(0)0, and 02(2)1-02(2)0) of natural 79/81Br12C14N have been recorded and analyzed in the 4.8-µm region using an FTIR spectrometer. Analyses of the same hot bands, previously recorded using a diode laser spectrometer, are also presented for the 13C and 15N isotopically labeled species. Copyright 1998 Academic Press.