The high-resolution infrared spectrum of HBF2: The 401 band near 926 cm−1

The type-C out-of-plane bending fundamental ν₄ (near 926 cm⁻¹) in the infrared spectrum of gaseous difluoroborane, HBF₂, has been recorded at high resolution. Rotational and centrifugal distortion constants have been obtained for the two isotopic species H¹⁰BF₂ and H¹¹BF₂ in both the ground and 4¹ levels. A small rotational perturbation in the 4¹ level of H¹¹BF₂ has allowed an estimate of the position of the ν₆ fundamental, which so far has not been observed directly.     

The high-resolution infrared spectrum of ethylene in the 1800–2350 cm−1 spectral region

Fourier transform spectra of ethylene (C₂H₄) have been recorded in the 1800–2350?cm^?1 (4.3–5.6?µm) spectral region using a Bruker IFS125HR spectrometer at a resolution of 0.004?cm^?1 leading to the observation of six vibrational bands, ν ₇?+?ν ₈, ν ₄?+?ν ₈, ν ₆?+?ν ₁₀, ν ₆?+?ν ₇, ν ₄?+?ν ₆ and ν ₃?+?ν ₁₀. The corresponding upper state ro-vibrational levels were fit using a Hamiltonian matrix accounting for numerous interactions. A satisfactory fit could be obtained using a polyad of nine interacting states {8¹10¹,?7¹8¹,?4¹8¹,?8¹12¹,?6¹10¹,?6¹7¹,?4¹6¹,?3¹10¹,?3¹7¹} of which three (8¹10¹, 8¹12¹ and 3¹7¹) are unobserved dark states. As a result a much more accurate and extended set of Hamiltonian constants were obtained than previously derived. The following band centers were determined: ν ₀(ν ₇?+?ν ₈)?=?1888.9783(20)?cm^?1, ν ₀(ν ₄?+?ν ₈)?=?1958.2850(20)?cm^?1, ν ₀(ν ₆?+?ν ₁₀)?=?2047.7589(20)?cm^?1, ν ₀(ν ₆?+?ν ₇)?=?2178.011(60)?cm^?1, ν ₀(ν ₄?+?ν ₆)?=?2252.8026(24)?cm^?1 and ν ₀(ν ₃?+?ν ₁₀)?=?2171.2397(20)?cm^?1. Finally, a synthetic spectrum that could be useful for ethylene detection in planetary atmospheres was generated.     

The infrared spectrum of gaseous cis-d2-ethylene below 1400 cm−1

Three infrared active fundamental bands of cis-d₂-ethylene have been studied at a resolution of ca. 0.030 cm⁻¹: the type-c band ν₇ and the two type-a bands ν₆ and ν₁₂. From a simultaneous analysis of infrared ground state combination differences due to ν₇ together with microwave measurements, a set of ground state rotational and centrifugal distortion constants has been obtained. For all three bands upper state spectroscopic constants are determined, and perturbations are identified. The K′_a = 4 level in ν₇ is perturbed locally by a higher order c-Coriolis resonance with ν₈. ν₆ is globally perturbed by first-order a-Coriolis resonances with ν₄ and ν₈. For ν₁₂ a higher order c-type Coriolis resonance with 2ν₁₀ is of importance for several K_a levels, and the constants for ν₁₂ have been obtained taking this interaction into account. In addition, a Coriolis resonance parameter and some constants for 2ν₁₀ have been determined.     

Fourier transform infrared spectrum of carbon disulphide in the 4ν2 + ν3 band region near 3100 cm−1

Fourier transform spectra have been recorded for carbon disulphide CS₂ in the region of the 4ν₂ + ν₃ band near 3100 cm^?1. The data analysis has determined new molecular constants. Bands were also observed for the isotopomer ¹²C³²S³⁴S.     

The near infrared overtone spectrum of propyne taken by diode laser in the 12700 cm−1region

Detailed regions of the near infrared spectrum of propyne between 12737 cm-¹ and 12778cm-¹ have been measured using a simple and inexpensive home-made laser diode spectrometer. This part of the spectrum covers the overlapping 3v₁ + v₃ + v₅ and 3v₁ + v₃ + v₅ + v₁₀—v₁₀ bands. Combining a global fit and an individual profile analysis made possible the determination of the vibrational and rotational constants in each band and in some cases the resolution of the individual K structure in each transition cluster.     

The high-resolution spectrum of water vapor between 13 200 and 16 500 cm−1

High-resolution Fourier transform spectra of water vapor between 13 200 and 16 500 cm⁻¹ have been analyzed, leading to a precise and extensive set of line positions, line intensities, and rotational energy levels of highly excited vibrational states.     

The infrared spectrum of isothiazole in the range 600–1500 cm−1, including a high-resolution study of the v 11(A′) band at 818 cm−1 and the v 16(A″) band at 727 cm−1, together with ab initio studies of the full spectrum

Abstract

The gas-phase high-resolution infrared spectrum of isothiazole in the range 600–1500 cm^?1 has been recorded, and revised band centres obtained for a number of vibrations. An analysis of the v ₁₁(A′) band at 818 cm^?1 and the v ₁₆(A″) band at 727 cm^?1 has been performed, using the Watson Hamiltonian, A-reduction, III^r representation. These were combined with previous microwave spectral data to provide combined analyses for rotational constants and quartic centrifugal distortion constants Δ _J , Δ _JK , Δ _K , δ _j and δ _K . These extend the knowledge derived from previous microwave and IR spectral studies. The equilibrium structures and the derived harmonic frequencies were calculated by ab initio methods, using a variety of basis sets with MP2, MP4 and CCSD(T) methods, and a comparison of these with experimental data is discussed. At a pragmatic level, the closest correlation of the rotational constants with experiment is not obtained with the most sophisticated methodology. Similarly, the vibration frequencies and intensities also vary strongly with the procedure. In particular, we found that the cc-pVTZ+MP2 results probably provide the best numerical comparison with experimental IR data for this molecule.     

The far infrared spectrum of trans-formic acid: An extension up to 175 cm−1

The far infrared spectrum of HCOOH was recorded at a high resolution (0.0009 cm^?1) and long path length (72 m) at the far-infrared beamline, Canadian Light Source. Spectra were recorded in the region 62–300 cm^?1, showing transitions from the trans-isomer.Ground state rotational transitions with K_a up to 30, were identified up to 175 cm^?1, extending the observation reported in the literature. A total of 3321 transitions were assigned and fitted together with previous (4149) published data. An improved set of rotational parameters was obtained adopting the symmetric top (A) reduction of the rotational Hamiltonian in the I^r representation. The newly measured far infrared transitions allowed the determination of all diagonal and off diagonal 8th order parameters L and of some of the diagonal 10th order parameters P.     

High-resolution infrared spectrum of hydrogen peroxide: The ν6 fundamental band

The infrared spectrum of the ν₆ asymmetric deformation band of hydrogen peroxide (H₂O₂) was studied in the region 1100–1350 cm⁻¹ using the two techniques of Fourier transform spectroscopy at 0.02 cm⁻¹ resolution and tunable diode laser spectroscopy at Doppler-limited resolution. Details of the wavelength calibration procedures adopted are discussed. For the first time, accurate values of the molecular parameters of this torsionally doubled, vibrational band were obtained. A total of 708 assigned transitions have been analyzed to yield a set of 14 rovibrational constants for the lower torsion-vibration level (SD = 0.00487 cm⁻¹) and 13 rovibrational constants for the upper torsion-vibration level (SD = 0.00382 cm⁻¹). These hybrid bands are primarily A type with band centers at 1264.5812 ± 0.0009 and 1273.6830 ± 0.0009 cm⁻¹. Because of the absence of observed perturbations, the derived molecular constants can be used to calculate transition frequencies with a high degree of accuracy up to K_a = 6.     

HSSH revisited: The high-resolution Fourier transform spectrum of the ground state between 30 and 90 cm−1

The spectrum of disulfane (HSSH) between 30 and 380 cm⁻¹ has been recorded in absorption using a new high-resolution Fourier transform spectrometer at the Justus-Liebig Universität Giessen. The spectrometer is briefly described, as well as procedures concerning the synthesis and handling of this quasi-stable species. A combined analysis of previous microwave data on the HSSH ground state and over 600 newly assigned lines between 30 and 90 cm⁻¹ has been carried out, yielding the effective spectroscopic parameters of the Watson S-reduced Hamiltonian. Examples of the strikingly simple perpendicular spectrum of this nearly symmetric prolate rotor are presented.     

The infrared spectrum of isoxazole in the range 600–1400 cm−l,including a high-resolution study of the v 7(A′) band at 1370.9 cm−1 and the v 16(A″) band at 764.9 cm−l,together with ab initio studies of the full spectrum

Abstract

The high resolution infrared gas phase spectrum of isoxazole in the range 600–1400 cm^?1 has been recorded and more precise centres obtained for a number of bands; analyses of the v ₇(A′) band at 1370.9cm^?1 and the v ₁₆(A″) band at 764.9cm^?1 have been performed. Use of the Watson Hamiltonian, A-reduction, III^r-representation and simultaneous analysis of the present IR and previous microwave data, has led to rotation constants and quartic centrifugal distortion constants Δ _J , Δ _JK , ΔK, δ _J and δ _K for the ground state and for the v ₁₆ vibrationally excited states. The equilibrium structures and the derived harmonic frequencies have been calculated by ab initio methods using triple zeta+polarization (TZVP) and cc-pVTZ basis sets, with MP2, MP4 and CCSD(T) methods. At each methodology, for closest numerical agreement between the calculated and observed rotation constants, the optimum basis set seems to be TZVP rather than cc-pVTZ basis sets. However, the order of the highest A″ and lowest A′ symmetry vibrations is only resolved by the cc-pVTZ basis set with the MP4 methodology, which does generate the experimental sequence (v ₁₄>v ₁₃) The CCSD(T) methodology does not lead to significant difference over either MP2 or MP4 with the TZVP basis set.     

The Raman spectrum of C2D4 near 1000 cm−1: The Coriolis coupled ν3 and ν6 bands

The Raman spectrum of deuterated ethylene C₂D₄ has been investigated in the 1000-cm⁻¹ regions. The close-lying (16 cm⁻¹ apart) ν₃ and ν₆ bands are perturbed by a Coriolis interaction around the c axis with |ζ₃₆^c| = 0.39. This interaction distorts both the anisotropy and the trace spectra, which are presented as recorded in Aarhus and Madrid, showing also computer simulation of the contours. A least-squares refinement of around 300 transitions allows the determination of the ν₃ and ν₆ band origins and rotational constants.     

The high-resolution spectrum of the ν1 (A1) band of 12CD3F

The spectrum of the ν₁ (A₁) band of ¹²CD₃F has been recorded with a resolution of 0.010 cm⁻¹ and deconvolved to 0.005 cm⁻¹. Over 1050 transitions have been assigned with K ≤ 16 and J ≤ 42. The spectrum is highly perturbed, exhibiting avoided crossings in most of the observed sub-bands. The origin of most of the local and global resonances has been determined and the coupling constants estimated. Due to the complexity of the spectrum resulting from the 24 potential interacting states in the region, the assigned frequencies were fitted in a restricted manner (K ≤ 3, J ≤ 15), to obtain the following effective constants for the band: ν₀ = 2090.8118(20) cm⁻¹, α^A = 1.19743 × 10⁻² cm⁻¹, and α^B = −1.8489 × 10⁻³ cm⁻¹. From an unrestricted least-squares analysis, fixing the above parameters the β's (D_v^x = D₀^x − β_v^x) were calculated to be β^J = 1.7776 × 10⁻⁷ cm⁻¹, β^JK = 8.3406 × 10⁻⁷ cm⁻¹, and β^K = −6.3829 × 10⁻⁷ cm⁻¹. These constants serve as good starting parameters for the global analysis necessary to fully analyze the 5-μm region of the ¹²CD₃F spectrum.     

The high-resolution spectrum of the ν1 + ν2 band of NO2: A spin-induced perturbation in the ground state

The spectrum of the ν₁ + ν₂ band of NO₂ has been studied with a resolution of 0.025 cm⁻¹. Spin-rotation constants and rotational constants are reported. An interesting perturbation has been found in the ground state of the molecule which occurs when the K_a = 0 and K_a = 2 levels become accidentally nearly degenerate around N = 42. An explanation of this interaction is presented.     

The absorption spectrum of 12C2H2 IV. The regions 7600–9200 cm−1 and 10600–11500 cm−1

The absorption spectrum of ¹²C₂H₂ has been recorded by intracavity laser absorption spectroscopy (ICLAS) in the 10600–11 500 cm^?1 spectral region, where no absorption bands were previously reported. Fifteen bands starting from the vibrational ground state are observed and rotationally analysed. All corresponding excited vibrational levels were assigned using the polyad model, the so-called cluster model (El Idrissi, M.I., Liévin, J., Campargue, A., and Herman, M., 1999, J. chem. Phys., 110, 2074) which allows vibrational energies, rotational B_v constants and, to some respect, relative band intensities to be predicted. Additional data and constants are also provided in the range 7600–9200cm^?1, whenever improving the literature results, from spectra recorded previously at ULB using Fourier transform spectroscopy. The assignment procedure in the range recorded by ICLAS is detailed, leading to a deeper understanding of vibration-rotation and intensity features of the absorption bands within the frame of the cluster model.     

The infrared spectrum of 12C2HD: the stretching–bending combination bands in the 1800–4700 cm−1 region

The infrared spectrum of ¹²C₂HD has been observed between 1800 and 4700?cm^?1 by Fourier transform spectroscopy. The ν₁, ν₂ and ν₃ absorption bands and the associated hot and combination bands involving the bending modes up to υ_t?=?υ₄?+?υ₅?=?2 have been investigated. Altogether, 60 vibrational bands were analysed, leading to the spectroscopic characterization of 31 vibrationally excited states. Several perturbations have been observed, but the transitions involving the perturbing states have not been detected. As a consequence, an appropriate treatment of the vibrational or ro-vibrational interactions has not been possible. A tentative assignment of the perturbing states has been proposed. Eventually, global fits for each fundamental vibration and its associated cold and hot bands have been performed.     

Infrared spectrum of the Ar-CO complex: observation of the v co = 2 ← 0 band at 4260 cm −1

The spectrum of the weakly-bound van der Waals complex Ar-CO has been observed for the first time in the region of the CO vibrational overtone, using a long-path (180 m) low-temperature (64 K) absorption cell and a Fourier transform infrared spectrometer. The appearance of the spectrum was very similar to that studied previously in the v _co = 1 ← 0 region. However, it was very much weaker, so a detailed analysis was only possible for the relatively uncongested K = 1 ← 0 and 0 ← 1 subbands. The parameters determined here for these sub-bands should help to constrain the C-O bond length dependence of the Ar-CO intermolecular potential in future theoretical models.     

Stimulated emission of atmospheric water vapour between 2 cm−1 and 30 cm−1 photoinduced by infrared radiation

Fourier spectra of humid air in a 0.8 m path when it was illuminated by a combined flux of millimetre waves, infrared and ultraviolet showed millimetre wave maser action pumped by the infrared component.