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The high resolution infrared spectrum of methylamine has been analyzed in the 40–720 cm −1 region (the ν 15  = 2←1 hot and ν 15  = 2←0 overtone bands) with a resolution of 0.00125 cm −1 . More than 14,400 rovibrational transitions (out of 133,000 spectral lines) for 0 ≤  K  ≤ 13 and K  ≤  J  ≤ 40 have been assigned using an original Loomis–Wood program dedicated to methylamine. A global fit of the torsional hot and overtone transitions has been carried out. The assigned transitions were fit to a single state model based on the group theoretical formalism of Hougen and Ohashi, which for the second torsional state seems to be at the limit of applicability. The standard deviation of the fit with K  ≤ 11 and J  ≤ 40 to 94 parameters was 0.006 cm −1 . [ABSTRACT FROM AUTHOR]

The torsional fundamental band of methylamine has been reassigned in a high resolution IR spectrum in the region from 40 to 360 cm −1 . Over 11,700 transitions with a resolution of 0.00125 cm −1 for 0 ⩽ K ⩽ 17 and K ⩽ J ⩽ 40 have been assigned. A global fit of the infrared, and previously assigned pure rotational and microwave data has been carried out and the band centre was determined at 264.583143(12) cm −1 . The combined data were fit to a single state model based on the group theoretical formalism of Hougen and Ohashi what resulted in the total standard deviation of 0.00079 cm −1 (0.31 MHz for the microwave spectrum). The set of 88 parameters allows for a reliable calculation of rovibrational levels for the first excited torsional state which will subsequently facilitate the analysis of numerous hot bands observed for methylamine. [ABSTRACT FROM AUTHOR]

The Doppler limited non-saturated rotationally resolved infrared spectra of the symmetric and asymmetric CH-stretch bands of CH 2 Br 2 have been measured. A continuous wave cavity ringdown setup with a widely tunable Mid-IR-OPO laser light source yielded a single-shot minimum absorption of 4.9 × 10 −8 cm −1 . In contrast to the heavily congested ν 1 band, the ν 6 band showed partially resolved rotational features that may serve as suitable absorption targets in future environmental detection schemes for CH 2 Br 2 . A straightforward, VPT2 (second-order vibrational perturbation theory) assisted quantum-chemical approach for assigning the rotational structure has been tested using different model chemistries. The molecular structures, anharmonic frequencies and the structural changes upon vibrational excitation of CH 2 Br 2 have been investigated. The predicted changes of the anharmonic rotational constants have been used together with available spectroscopic ground state constants to simulate the rovibrational structures of the ν 1 and ν 6 bands of CH 2 Br 2 . A refined analysis of the ν 6 band is presented yielding accurate values for the band origin and the rotational constants. A fit of the line positions of 312 prominent transitions of the three isotopologues revealed a low standard error of 0.00056 cm −1 , hence within the absolute 0.0009 cm −1 wavelength accuracy of the used spectrometer setup. A combined analysis of the predicted line strengths and positions of the strong Q sub-branches of the ν 6 band has been performed to test the ability of the different density functionals for VPT2 prediction of anharmonic molecular constants. The M06/6-311++G(d,p) model chemistry turned out to yield reliable state-dependent rotational constants that are accurate enough to reproduce the overall rotational structure even without fitting. [ABSTRACT FROM AUTHOR]

Abstract: The absorption spectrum of propyne (CH3CCH) has been investigated in the range 6200–6700cm−1. Data were obtained using three different experimental techniques: conventional FTIR experiments (room temperature, 0.018cm−1 resolution, 10m absorption path), FTIR experiments using a femtosecond broadband absorption source and a build up cavity (room temperature, 0.02cm−1 resolution, absorption path between 1500 and 12,000m), cavity ring down spectroscopy to probe a propyne/Ar supersonic expansion (T rot ≈20K, sub-Doppler resolution, 720m effective absorption path length). The analysis focused on one perpendicular () and four parallel (2ν 1, ν 1 + ν 2, ν 1 + ν 3 + ν 5, ) bands, all perturbed by a complex system of Coriolis and anharmonic interactions. A model Hamiltonian was built, including all symmetry allowed perturbations between the upper levels of the studied bands but not accounting for additional interacting states. In total 1176 rovibrational transitions have been assigned and simultaneously fitted (σ =0.0029cm−1), leading to a set of effective rovibrational parameters. The resulting polyad structure is discussed and additional bands identified in the spectral range are tentatively assigned. [Copyright &y& Elsevier]

Abstract: For the first time the C–N stretching band of methylamine has been assigned in a high resolution spectrum in the region from 960 to 1200cm−1. Over 3500 transitions with a resolution of 0.001cm−1 for K from 0 to 12 have been assigned. A global fit has been made and the band center was determined at 1044.8134(33)cm−1. Several branches of the C–N band are strongly perturbed through Fermi and Coriolis type resonances. The sources of the perturbations have been identified – the fourth torsional state 4ν 15 and the combination state ν 9 + ν 15. An attempt to fit the observed transitions to a single state model based on the group theoretical formalism of Ohashi and Hougen resulted in the standard deviation of 0.04cm−1. [Copyright &y& Elsevier]

Abstract: The first validated detection of the elusive diazirinone molecule (N2CO) in the gas phase was performed using high-resolution infrared spectra recorded in the 1810–2100cm−1 region. The ν 1 and 2ν 5 bands were identified at 2043.8 and 1863.3cm−1 close to the ab initio prediction [X.Q. Zeng, H. Beckers, H. Willner, J.F. Stanton, Angew. Chem. Int. Ed. 50 (2011) 1720–1723]. For these two bands, the individual lines exhibit a (2:1) intensity alternation, confirming a three membered ring structure (C2V symmetry) for N2CO. The major output of the ν 1 and 2ν 5 bands analysis is the first experimental determination of the ground-state rotational constants of cyclic N2CO. The observed intensity pattern of the ν 1 and 2ν 5 bands is in agreement with the existence of a strong Fermi resonance coupling the 11 and 52 energy levels. [Copyright &y& Elsevier]

Abstract: The region of the infrared-active band of the ν9 CH2 bending mode [1.1.1]propellane has been recorded at a resolution (0.0025cm−1) sufficient to distinguish individual rovibrational lines. This region includes the partially overlapping bands ν9 (e′)=1459cm−1, 2ν18 (l =2, E′)=1430cm−1, ν6 +ν12 (E′)=1489cm−1, and ν4 +ν15 (A 2″)=1518cm−1. In addition, the difference band ν4 −ν15 (A 2″) was observed in the far infrared near 295cm−1 and analyzed to give good constants for the upper ν4 levels. The close proximities of the four bands in the ν9 region suggest that Coriolis and Fermi resonance couplings could be significant and theoretical band parameters obtained from Gaussian ab initio calculations were helpful in guiding the band analyses. The analyses of all four bands were accomplished, based on our earlier report of ground state constants determined from combination differences involving more than 4000 pairs of transitions from five fundamental and four combination bands. This paper presents the analyses and the determination of the upper state constants of all four bands in the region of the ν9 band. Complications were most evident in the 2ν18 (l =2, E′) band, which showed significant perturbations due to mixing with the nearby 2ν18 (l =0, A 1′) and ν4 +ν12 (E′) levels which are either infrared inactive as transitions from the ground state, or, in the latter case, too weak to observe. These complications are discussed and a comparison of all molecular constants with those available from the ab initio calculations at the anharmonic level is presented. [Copyright &y& Elsevier]

The assignment of the wagging band, ν9, of methylamine was extended to weak and perturbed series in a new high-resolution spectrum in the region from 640 to 960 cm-1 with extensive use of new Loomis-Wood software for Windows for the LAV molecules. Compared with previous reports, the number of assigned transitions in the wagging band (13,000) has been doubled. Most series extend as far as J = 40, even for symmetry species of lower statistical weight. For low K values (K ' = 0 and 1), even transitions of mixed type, E1+1↔E1-1, have been observed. Several branches are strongly perturbed by Fermi and Coriolis-type resonances. An attempt to fit the observed transitions to a single-state model resulted in a standard deviation of 0.018 cm-1. [ABSTRACT FROM AUTHOR]

Abstract: A high resolution vibration–rotation spectrum of deuterated monobromoacetylene (DCCBr) has been recorded with a Bruker IFS 120 Fourier Spectrometer in the wavenumber region 1700–2800cm−1, which covers the C–D and Cing fundamental (ν 1 and ν 2, respectively) and the Cx2013;Br stretching vibrational combination (ν 2 + ν 3) band systems. The analysis of the spectrum provides accurate vibrational term values and rotational constant for 20 vibration–rotation bands for both isotopic species, DCC79Br and DCC81Br. [Copyright &y& Elsevier]

• Spectroscopic ro-vibration analysis of the 3ν 2 /ν 2 +ν 4 dyad of 15NH 3. • 5770 rotation-inversion and vibration-rotation-inversion transitions are assigned. • Transitions involve the s, a inversion levels of v 2 = 3 and v 2 = v 4 = 1 states. • All transitions are fitted simultaneously using a rotation-inversion Hamiltonian. • Accurate spectroscopic parameters are obtained for v 2 = 3 and v 2 = v 4 = 1 a, s states. The a, s inversion levels of v 2 = 3 and v 2 = v 4 = 1 vibration states of 15NH 3 are studied from high resolution infrared spectra up to 3200 cm−1. Spectra were recorded from 60 to 2000 cm−1 using the Bruker IFS 125 interferometer located at the Canadian Light Source and from 1900 to 3200 cm−1 using the Bomem DA 008 in Bologna. Transitions in 3ν 2 and ν 2 +ν 4 , in the 3ν 2 ← ν 2 , ν 2 +ν 4 ← ν 2 , 3ν 2 ← 2ν 2 , ν 2 +ν 4 ← 2ν 2 , 3ν 2 ← ν 4 , ν 2 +ν 4 ← ν 4 , and 3ν 2 ↔ ν 2 +ν 4 hot bands, and the rotation-inversion transitions in 3ν 2 and ν 2 +ν 4 have been observed. 5770 transitions with J max ′ / K max ′ up to 15 have been assigned, including 395 perturbation allowed ones. All transitions were fitted simultaneously on the basis of a rotation-inversion Hamiltonian which includes distortion constants up to 10th power in the angular momentum and all symmetry allowed interaction parameters between and within the a, s inversion levels of v 2 = 3 and v 2 = v 4 = 1. The term values of the lower levels of transitions have been calculated using the parameters recently derived for the ground and v 2 = 1, 2 and v 4 = 1 states. The data were reproduced at experimental accuracy. The results are compared with those of 14NH 3. The experimental transitions are compared with their theoretically predicted values. The list of assignments is supplied as supplementary material. The present results noticeably improve the wavenumber line list in the HITRAN 2016 data base. Image, graphical abstract [ABSTRACT FROM AUTHOR]