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.     

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.     

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.     

Vibrational spectra and force constants of symmetric tops—XLII. Rovibrational spectra of CF3I in the ν2, ν3, 2ν3 and ν2 + ν3 regions

The gas phase i.r. spectrum of CF₃I has been investigated in the ν₂, ν₃, 2ν₃ and ν₂ + ν₃ region with a resolution of 0.04 cm⁻¹. Rotational J clusters have been resolved, and several vibrational and rovibrational parameters of ν₂, 743.364(8) cm⁻¹ and ν₃, 286.303(3) cm⁻¹, have been determined by polynomial methods and by band contour simulation.     

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.     

Infrared diode laser spectroscopy of the ν2(2+ ← 1−) band of H3O+

Rotational lines in the ν₂ = 2⁺ ← 1⁻ “hot” band of the inversion mode of the oxonium (H₃O⁺) ion have been recorded by diode laser absorption spectroscopy. The ion was generated in low pressure gas discharges and detected using both velocity modulation and modulated hollow cathode techniques. Analysis of the spectra using a simple oblate symmetric top model has allowed the rotational parameters describing the 2⁺ inversion state to be determined for the first time. The band origin lies at 521.4383(52) cm⁻¹. These data will be useful in refining the oxonium ion inversion potential function and should aid in the analysis of other bands involving or perturbed by the 2⁺ level.     

Analysis of the ν2 :ν3 + ν4 Fermi resonance in CH3CN isotopic species in solution

Infrared bands due to ν₃ + ν₄, ν₂, ν₃ and ν₄ were recorded for the species CH₃CN, ¹³CH₃CN, CH₃¹³CN and CH₃C¹⁵N in the solvents carbon tetrachloride, chloroform, benzene, pyridine and dimethyl sulphoxide. Values of W₂₃₄ were extracted by the modified Winther method, which are slightly less, 11.2–11.9 cm⁻¹, than the value in the gas, 12.15 cm⁻¹. Relative intensity measurements of ν₃ + ν₄ and ν₂ in CCl₄ are compatible with an unperturbed intensity ratio, I_{ν3 + ν4}/ I_ν2 of ∼ 0.03. The fallibility of the infrared intensity method for determining W, and the need for precise frequency data in the Winther method, are stressed.     

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.     

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.     

FTIR spectra of the 2ν4, ν4 + ν6 and 2ν6 bands of formaldehyde

High resolution IR spectra of the overtones and the combination band of the ν₄ and ν₆ modes of formaldehyde (2ν₄, ν₄ + ν₆ and 2ν₆) were measured in the region of 2200–2650 cm⁻¹ using FTIR. The combination band ν₄ + ν₆, whose dipole transition is forbidden from molecular symmetry, was observed due to the intensity borrowed from the other bands. The observed frequencies were analysed by a Hamiltonian in which A-type Coriolis interactions and Darling—Dennison interaction were taken into account. The ratio and the relative signs of the transition dipole moments of the overtone bands, μ_2ν4 and μ_2ν6, have been determined by analysing the intensity distribution of the vibration—rotation lines.     

Radiative lifetime of CO+ (X2∑+, ν) ions

The radiative relaxation of CO⁺(X²∑⁺, ν) ions produced by ionization of CO and of OCS with 70 eV electrons has been investigated using the monitor ion technique in a triple FT ICR spectrometer. Since the monitor reaction is exothermic for ν ≥ 1, the experimental lifetimes, 170 ms for CO⁺ from CO and 210 ms for CO⁺ from OCS, should correspond to the overall decay rate of ν ≥ 2 with a small contribution of ν = 1.These values being much larger than the theoretical lifetime of ν = 1 (128.5 ms), computer-simulated overall lifetimes for ν ≥ 1 and ν ≥ 2 have been determined using theoretical lifetimes calculated by Rosmus and Werner and a vibrational population deduced from photoelectron spectroscopy of CO with 40.8 eV photons (Gardner and Samson). The computer-simulated lifetimes, 250 ms for ν ≥ 1 and 125 ms for ν ≥ 2, are indeed about twice as large as the theoretical lifetimes for ν = 1 and ν = 2, respectively, indicating that the large experimental lifetimes may be accounted for by radiative cascade from the upper vibrational levels.     

Rotational and rovibrational spectroscopy of CH3NC of the ground and ν4 = 1 vibrational states

The parallel vibration-rotation band ν(4) of methyl isocyanide (CH(3)NC), with a band center at 944.9 cm(-1), was studied by FTIR spectroscopy between 890 and 980 cm(-1) in order to improve the ground-state rotational constants. Such improvement is essential for the scheduled studies of excited vibrational levels and their mutual anharmonic resonances occurring at higher values of the K rotational number. Ground-state combination differences generated from this band, spanning values of J/K from 0 to 85/13, were combined with rotational data from the literature and newly measured rotational transitions, extending the J/K range from 3/0 up to 31/14, and fitted simultaneously with a fully quantitative reproduction of the data. The infrared data of the ν(4) band were analyzed together with rotational data of the ν(4) = 1 level, spanning values of J/K from 4/0 to 14/12. The fit in the approximation of an isolated vibrational state, with the transitions perturbed by weak local resonances excluded, yields reproduction of the data within experimental uncertainties.     

Infrared emission spectrum of HNO: The ν1 band

HNO has been observed in emission from a radiofrequency discharge through a mixture of ammonia and oxygen. The ν₁ (NH stretching) band in the region 2400–3200 cm⁻¹ has been recorded with a Fourier transform spectrometer using an apodized resolution of 0.04 cm⁻¹. The analysis of the band has been extended to higher K values than in earlier work.     

Fourier transform infrared isotopic study of ZnC3: identification of the ν1(a') mode

An isomer of ZnC(3) with bent structure in its (1)A(') electronic state has been detected in the products from the dual laser ablation of carbon and zinc rods that were trapped in solid Ar at ~12 K. Measurements of (13)C isotopic shifts have enabled the identification of the ν(1)(a(')) asymmetric carbon stretching fundamental at 1858.9 cm(-1). The experimental results are in good agreement with the predictions of DFT-B3LYP/6-311G(d) calculations that indicate a singlet bent isomer ground state structure with triplet linear and singlet cyclic isomers lying slightly higher in energy. This is the first optical detection of any isomer of ZnC(3).     

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.     

Crystallographic study of YCo3+1−2xCo2+xPt4+xO3 and DyCo3+1−2xCo2+xPt4+xO3

The crystal structures of single crystals of YCo³⁺_.36Co²⁺_.32Pt⁴⁺_.32O₃ and DyCo³⁺_.36Co²⁺_.32Pt⁴⁺_.32O₃ have been examined at room temperature, and shown to be isostructural with GdFeO₃, which belongs to space group Pbnm. The overall expansion of octahedra caused by substitution of platinum enhances the distortion of rare-earth dodecahedra by moving 4 out of 12 oxygens further away from the rare-earth ions, as shown by the rotation of octahedra along the [110] axis. No order has been found for Co²⁺, Co³⁺, and Pt⁴⁺.     

Vibration-rotation infrared spectrum of ν2 of methyl iodide—Coriolis interaction with ν5

Vibration-rotation i.r. spectrum of ν₂ of methyl iodide was measured with a resolution of 0.08 cm⁻¹. The spectrum was analyzed by taking account of an xy-type Coriolis interaction between ν₂ and ν₅ and a Fermi resonance between ν₅ and ν₃ + ν₆. The analysis gave values of spectroscopic parameters which include (ν₀)₂ 1251.193 cm⁻¹, A₂-A₀ 0.02030 cm⁻¹, (D_J)₂ 2.08 × 10⁻⁷ cm⁻¹, (D_JK)₂ 3.2 × 10⁻⁶ cm⁻¹ and ζ_2,5a^y −0.630₅.     

Fourier transform infrared isotopic study of linear MnC3: identification of the ν1(σ) fundamental

Linear MnC(3) has been detected in the products from the dual laser ablation of carbon and manganese rods trapped in solid Ar at ～12 K. The ν(1)(σ) vibrational fundamental, an asymmetric carbon stretching mode, has been identified at 1846.9 cm(-1). Fourier transform infrared measurements of (13)C isotopic shift are in good agreement with the predictions of density functional theory calculations using the mPW1PW91 functional with 6-311+G(3df) basis set. This is the first optical detection of the linear isomer of MnC(3) for which previous photoelectron spectroscopy studies have reported evidence of a cyclic isomer.