Study of the ν1, ν1 + ν3 and ν2 + ν3 infrared bands of ONCl

A type (ΔK_a = 0) rovibrational lines of the near-prolate asymmetric top ¹⁶O¹⁴N³⁵Cl have been assigned on high resolution Fourier transform spectra: 820 lines of the ν₁ band, centered around 1800 cm⁻¹, 435 lines of the ν₁ + ν₃ band, centered around 2131 cm⁻¹, and 257 lines of the ν₂ + ν₃ band, centered around 925 cm⁻¹. Least-squares calculations have been carried out over these lines, using the A reduced Watson's hamiltonian in I^r representation; r.m.s. standard deviations of 0.0016 cm⁻¹, 0.0016 cm⁻¹ and 0.006 cm⁻¹ have been respectively obtained, making it possible to measure molecular constants of the (001), (101) and (011) vibrational levels of ¹⁶O¹⁴N³⁵Cl.     

Rotational spectrum of SiC2 in the ν3 excited state

The rotational spectra of SiC₂ in the vibrationally excited states of the ring deformation mode (υ₃ = 1, 2) were observed in the frequency region of 140–400 GHz by using a source-modulated microwave spectrometer combined with a free space absorption cell. SiC₂ was produced in the cell by discharging a mixture of SiH₄, C₂H₂ and CO. Least-squares analysis of the observed spectral lines yielded the rotational constants and the centrifugal distortion constants precisely. Sextic, octic and decatic centrifugal distortion constants were required in the least-squares fit in order to get a good fit of the observed frequencies to those calculated within experimental errors. The inertial defects for the υ₃ = 1 state and the υ₃ = 2 state do not show a linear dependence on the vibrational quantum number. The quartic centrifugal distortion constants, Δ_JK, Δ_K and δ_K, are abnormally large, and show a large change on the vibrational states. These abnormal behaviours are interpreted in terms of a large amplitude motion of the ν₃ mode.     

Diode laser i.r. spectrum and rovibrational analysis of CF3Br in the ν2 + ν3 region

The gas phase i.r. spectrum of CF₃Br, with natural isotopic abundance, has been investigated in the ν₂+ ν₃ region near 1120 cm⁻¹ using a tunable diode laser spectrometer. The measurements have been carried out at low temperature (⋍ 200 K) to minimize the effects due to the “hot” band absorptions. The K structure of many P(J) and R(J) manifolds has been resolved and analyzed: the maximum J value reached for individual lines was 62 and 70 for CF₃⁷⁹Br and CF₃⁸¹Br, respectively. The identified transitions have been used in a least-squares fit to the energy expression up to the quartic terms and molecular parameters for the ν₂ + ν₃ combination have been obtained. Residual weak features due to “hot” bands of ν₃ and ν₆ have been assigned; the J structure has been analyzed by means of a polynomial procedure and spectroscopic constants for both the isotopomers have been derived.     

Rovibrational study of the ν2 + ν±14, ν2 + 3ν±16, ν1 + ν±15, ν±14 + ν±15, ν±14 + ν±5, ν±5 + 3ν±16, ν±5 + 3ν±36 and ν1 + ν2 infrared bands of CH335Cl studied in a high-resolution FTIR spectrum from 4250 to 4600 cm−1

About 6400 lines belonging to the ν₂ + ν^±1₄, ν₂ + 3ν^±1₆, ν₁ + ν^±1₅, ν^±1₄ + ν^±1₅, ν^±1₄ + ν^±₅, ν^±₅ + 3ν^±1₆ and ν^±₅ + 3ν^±3₆ bands have been assigned. An r.m.s. deviation of 0.047 cm⁻¹ has been achieved by a least-squares fit of 1427 lines. For this purpose, a simplified model, taking into account five anharmonic resonances already found in a previous work [Molec. Phys. 70, 849 (1990)] and the well known x-y Coriolis resonance between the ν₂ and ν₅ modes of methyl halides, was used. Although not observed, the ν^±1₄ + ν^±1₅ and ν₁+ ν₂ parallel bands are strongly coupled by Coriolis resonance to ν₂ + ν^±1₄ and ν^±1₅ respectively. A few secondary resonances remain unexplained in several parts of the spectrum.     

Study of the ν2 + ν3 infrared band of ONCl

Two hundred and sixty A type rovibrational lines of the ν₂ + ν₃ vibrational band of ¹⁶O¹⁴N³⁵Cl, around 925 cm⁻¹, have been assigned; a least-squares calculation with a r.m.s. deviation of 0.0006 cm⁻¹ has made it possible to measure several constants of the (011) vibrational level.     

High resolution quantum cascade laser studies of the ν3 band of methyl fluoride in solid para-hydrogen

Spectra of solid para-H(2) doped with CH(3)F at 1.8 K are studied in the ν(3) region (~1040 cm(-1)) using a quantum cascade laser source. As shown previously, residual ortho-H(2) in the sample (~1000 ppm) gives rise to distinct spectral features due to clusters of the form CH(3)F-(ortho-H(2))(N), with N = 0, 1, 2, 3, etc. Brief annealing at 7 K is found to give narrower spectral lines (≥0.006 cm(-1)) than conventional (5 K) annealing, and causes the N = 3 and 4 lines to fragment into two or more components. The N = 3 line is observed to be particularly stable and persistent. The N = 0 line (no ortho-H(2) neighbors) is resolved into two closely spaced (≈0.007 cm(-1)) components which are assigned to the K = 0 and 1 states of CH(3)F rotating around its C(3v) symmetry axis (ortho- and para-CH(3)F, respectively). Similar K-structure is also evident for other lines. Weak but persistent features ("N = 1/2 lines") are observed mid way between N = 0 and 1.     

Study of the spectrum of CH379Br between 1520 and 1700 cm−1: The ν3 + ν6 and the ν5 rovibrational bands

The ν₃ + ν₆ band of CH₃ ⁷⁹Br has been directly analyzed for the first time, and an r.m.s. standard deviation of 0.0035 cm⁻¹ was obtained over 394 lines of K″ΔK = 2 up to 12, through a least-squares calculation using an unperturbed model. Nevertheless discrepancies occur on sub-bands with K″ ⩾ 9, which remain not yet understood. In particular it seems difficult to explain them by a Fermi resonance with the ν₅ band, since it has been possible to fit properly around 580 lines of this band, belonging to sub-bands K″ΔK = 7 up to 16, taking only into account the Coriolis resonance with the ν₂ band and the l(2,2) resonance of ν₅.     

Temperature dependence of nitrogen broadening of ozone ν3 rovibrational transitions

We report N₂-broadening coefficients for rovibrational transitions of the ν₃ band of ozone in the temperature range 180–296 K. We assume a power law dependence of the temperature for these coefficients, with a temperature exponent n. For the 21 transitions we measured, the average value of n is 0.74 and is well within experimental error of the theoretically predicted value of 0.77. The significance of this parameter in modeling atmospheric IR absorbance due to ozone is discussed.     

Note: Deperturbation of the ν3 band of BeD2

High rotational levels of the 001 (Σ(u)) state of BeD(2) are perturbed by the nearby 03(3)0 (Φ(u)) state. Deperturbation analysis results in an experimental value for the vibrational energy of the 030 level.     

On some controversy regarding νOH assignments in CsH2PO4

Spectroscopic methods such as Raman scattering and IR absorption, as well as structural methods such as x-ray and n-diffraction, offer rather ambiguous interpretation of the high-frequency phonon spectrum of CsH₂PO₄ (CDP), especially regarding the proper assignment of proton vibrational modes. Empirical lattice dynamics (LD) simulations of the proton vibrational density of states ((H-VDOS)) in CDP also reveal a discrepancy in the frequency assignments of the OH stretching modes of its two non-equivalent hydrogen bonds. This may be resolved by accounting for the LD simulated directional (H-VDOS) along the three Cartesian axes of CDP, from which the corresponding anisotropy of the proton kinetic energy tensor can be deduced. The results may then be tested by a simple deep inelastic neutron scattering (DINS) measurement on a single crystal of para-electric CDP at room temperature.     

Comparison and assessment of procedures for calculating the R(12) line strength of the ν1 + 2 ν2 + ν3 band of CO2

Recently, results for the CO(2) R(12) line strength parameter have been reported, which differ significantly and are inconsistent with respect to quoted uncertainties. We investigate to what extent this inconsistency might be caused by the chosen data analysis methods. To this end, we assess and compare a parametric fitting procedure and a non-parametric approach. We apply the methods to simulated and measured line spectra, and we specify the conditions required for the safe application of the two procedures. For our present data, the corresponding conditions are satisfied for both methods, and consistent results are obtained. However, the simulations reveal that the fitting procedure can show shortcomings when the uncertainty in the wavenumber is large.     

α BB Resonance in the ν8 Band of Borazine –10B

The high-resolution FTIR spectrum of the fundamental ₈ of borazine ¹⁰B₃ ¹⁴N₃ ¹H₆ was reanalyzed taking into account the ^BB resonance with the combination band (₁₀ + ₁₇). A parameter set for the states ₈ = 1 and ₁₀ = ₁₇ = 1, respectively, is given, reproducing the observed spectrum at least up to J = 30 with experimental accuracy.     

Measurements of the absorption line strength of hydroperoxyl radical in the ν3 band using a continuous wave quantum cascade laser

Mid-infrared absorption spectroscopy has been applied to the detection of the hydroperoxyl (HO(2)) radical in pulsed laser photolysis combined with a laser absorption kinetics reactor. Transitions of the ν(3) vibrational band assigned to the O-O stretch mode were probed with a thermoelectrically cooled, continuous wave mid-infrared distributed feedback quantum cascade laser (QCL). The HO(2) radicals were generated with the photolysis of Cl(2)/CH(3)OH/O(2) mixtures at 355 nm. The absorption cross section at each pressure was determined by three methods at 1065.203 cm(-1) for the F(1), 13(1,13) ← 14(1,14) transition in the ν(3) band. From these values, the absolute absorption cross section at zero pressure was estimated. The relative line strengths of other absorptions in the feasible emitting frequency range of the QCL from 1061.17 to 1065.28 cm(-1) were also measured, and agreed with values reproduced from the HITRAN database. The ν(3) band absorption strength was estimated from the analytically obtained absolute absorption cross section and the calculated relative intensity by spectrum simulation, to be 21.4 ± 4.2 km mol(-1), which shows an agreement with results of quantum chemical calculations.     

Temperature dependence of broadening and shifts of methane lines in the ν4 band

We have recorded high-resolution absorption spectra of methane broadened by dry air and by N₂ at temperatures from −63 to 41°C using a Fourier transform spectrometer. These spectra have been analyzed to determine pressure broadening and line-shift coefficients, along with their temperature dependences, for 148 lines in the ν₄ fundamental band of ¹²CH₄. The experimental uncertainties for lines with J″≤10 are generally <2% for the broadening coefficient b⁰_L, 6–12% for its temperature dependence exponent n, 6–20% for the line-shift coefficient δ⁰, and 20–40% for its temperature dependence coefficient δ′; for J″> 10 the experimental uncertainties are somewhat larger. These results, especially for N₂-broadening, are in excellent agreement with other recent measurements. Since the present results cover a wide range of rotational quantum numbers (J″ up to 14), the variation of the temperature dependence of the half-widths and shifts from line to line within the ν₄ band is also examined.     

Isotopic ratio νHX/νDX of hydrogen halide complexes in solid argon

The wavenumbers of the ν_HCl band in B… HCl complexes and of the central HF bond in B… (HF)₂ complexes in solid argon have a minimum value     

Line-width temperature dependence of selected R-branch transitions in the ν3 fundamental of 14N216O between 135 and 295 K

The temperature dependence of N₂ foreign gas broadening coefficients for eight R-branch transitions in the ν₃ fundamental of ¹⁴N₂¹⁶O have been measured at 135, 176, 210 and 295 K by tunable diode laser spectroscopy. In approximate agreement with the theoretical value of 0.75 for n in the relation γ⁰_L(T)/γ⁰_L(T₀) = (T₀/T)ⁿ for quadrupole—quadrupole collisional interactions, n ranged from 0.66 to 0.71. We observed a distinct dependence between J and the exponent n in the range between R(15) and R(43).     

High-resolution FTIR spectroscopy of the ν8 and Coriolis perturbation allowed ν12 bands of ketenimine

High resolution FTIR spectra have been recorded in the region 250-770 cm(-1) using synchrotron radiation and over 2000 transitions to the ν(8) and ν(12) states of the short lived species ketenimine have been assigned. Ground state combination differences combined with published microwave transitions were used to refine the constants for the ground vibrational state. Rotational and centrifugal distortion parameters for the v(8) = 1 and v(12) = 1 levels were determined by co-fitting transitions, and treating a strong a-axis Coriolis interaction. Selection rules for the observed ν(12) transitions indicate that they arise solely from "perturbation allowed" intensity resulting from this Coriolis interaction.     

High-resolution Fourier-transform infrared spectroscopy of the ν6 and Coriolis perturbation allowed ν10 modes of ketenimine

High-resolution FTIR spectra of the short lived species ketenimine have been recorded in the region 700-1300 cm(-1) and over 1500 transitions of the ν(10) and ν(6) modes have been assigned. Effective rotational and centrifugal distortion parameters for the v(10) = 1 and v(6) = 1 (excluding K(a) = 5) states were determined by co-fitting transitions, and treating strong a- and c-axis Coriolis interactions between them. Other perturbations attributed to interactions with the v(8) = 2 and v(12) = 1 + v(8) = 1 dark-states were also observed and treated. The ν(10) transitions are predicted to be inherently very weak, but are enhanced by an intensity stealing effect with the highly IR active ν(6) mode. A mechanism for this intensity stealing in ketenimine is also detailed.     

ℓ-Resonance effects in the νv5, 2ν5←ν5, and ν4 + ν5←ν4 bands of C2H2 and 13C12CH2 near 13.7 μm

An extension to the previous LSCD (lower state combination difference) determination of molecular parameters involving acetylene's ν₅ fundamental and the strongest one quantum hotbands, 2ν₅←ν₅ and ν₄ + ν₅←ν₄ [J. Molec. Spectrosc. 146, 389 (1991)] has been made. A novel iterative numerical diagonalization procedure was employed to fit the vibrational states involved in the seven one quantum hotbands. This method utilizes the Hellmann—Feynman theorem to calculate first derivatives and singular value decomposition (SVD) in its least-square procedure and permits the simultaneous evaluation of the effective dipole moment responsible for the ℓ-type resonance effect upon IR intensities. A set of molecular parameters describing the rotation—vibration levels of the ground state, ν₅, ν₄, 2ν₅ and ν₄ + ν₅ for the major isotope and for ¹³C¹²CH₂ are reported based upon FT-spectrometric data taken at the McMath Solar Telescope Observatory. The improved spectroscopic parameters retrieved from this investigation will serve as a database for modelling abundances of acetylene in various astrophysical sources.