High-resolution Fourier transform infrared spectroscopy and analysis of the ν12 fundamental band of ethylene-d4

The Fourier transform infrared (IR) spectrum of the ν₁₂ fundamental band of ethylene-d₄ (C₂D₄) has been measured with an unapodized resolution of 0.004 cm⁻¹ in the frequency range of 1030–1130 cm⁻¹. A total of 1340 assigned transitions have been analyzed and fitted using a Watson's A-reduced Hamiltonian in the I^r representation to derive rovibrational constants for the upper state (v₁₂=1) up to five quartic terms with a standard deviation of 0.00042 cm⁻¹. They represent the most accurate constants for the band thus far. The ground state rovibrational constants were also further improved by a fit of combination–differences from the IR measurements. The relatively unperturbed band was found to be basically A-type with a band centre at 1076.98492±0.00003 cm⁻¹.     

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.     

High resolution i.r. spectrum of the ν1 band of HCCCl

The ν₁ spectrum of HCCCl was studied at a resolution of 0.045 cm⁻¹. Six bands were assigned and analyzed, two for the Cl³⁷ and four for the Cl³⁵ isotope. Band constants obtained for the six bands are listed. The ν₁ + ν₅ ← ν₅ band is unusually intense on the P side.     

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.     

The analysis of high-resolution spectra of the ν2 and ν5 bands of CH335Cl and CH337Cl

The ν₂ and ν₅ bands of CH³₃⁵Cl and CH³₃⁷Cl between 1300 and 1600 cm⁻¹ have been analysed using a Fourier transform spectrum with 0.006 cm⁻¹ resolution. For CH³₃⁵Cl, the microwave data and 1200 lines from the IR spectrum with J⩽ 50 were fitted with an overall r.m.s. error of 0.00079 cm⁻¹ using the method of predicative observations. A similar fit for 900 lines of CH³₃⁷Cl gave an overall r.m.s. error of 0.00055 cm⁻¹, providing erroneous microwave data on the ν₅ level are omitted. Improved molecular constants are reported for both isotopic species. As expected, the values for ν₂ and ν₅ are little affected by chlorine isotopic substitution.     

High-resolution Fourier transform infrared absorption spectroscopy of the ν6 band of c-C3H2

The gas-phase high-resolution absorption spectrum of the ν(6) band of cyclopropenylidene (c-C(3)H(2)) has been observed using a Fourier transform infrared spectrometer for the first time. The molecule has been produced by microwave discharge in an allene (3.3 Pa) and Ar (4.0 Pa) mixture inside a side arm glass tube. The observed spectrum shows a pattern of c-type ro-vibrational transitions in which the Q-branch lines strongly and distinctly stand out in the spectrum. A combined least-squares analysis of the observed 216 ro-vibrational transitions together with 28 millimeter-wave rotational transitions from the previous study has resulted in an accurate determination of the molecular constants in the ν(6) state. The band center is found to be at 776.11622(13) cm(-1) with one standard deviation in parentheses, which is 2.3% lower than the matrix isolation value. The intensity ratio I(3)(ν(3))/I(6)(ν(6)) obtained from the observed ν(3) and ν(6) bands, 1.90(9), is somewhat lower than the ratio estimated from ab initio (2.4-2.6) and DFT (2.8) calculations.     

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 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 Lα X-ray fluorescence spectra of palladium compounds

High-resolution Pd Lα (L₃–M_4,5) X-ray fluorescence spectra of several Pd compounds were measured on a double-crystal X-ray fluorescence spectrometer. It was found that the chemical shifts of Pd Lα₁ line in Pd metal, Pd–Ag alloy, PdCl₂, PdBr₂, PdI₂, Pd(NO₃)₂ and Pd(acac)₂ were relatively small (less than 0.1 eV with metallic Pd as reference). We adopted the charge transfer effect to elucidate this seemingly anomalous experimental result. For divalent Pd, at the moment of the creation of a 2p⁻¹ core hole, one or two electrons were transferred from the ligand to the central Pd atom. Therefore the divalent Pd (II, 4d⁸) may have valence electron configuration similar to metallic Pd (0, 4d¹⁰), and this eventually results in the small chemical shifts.     

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.     

Determination of mechanisms of the ν1(H–F) band shape formation in the absorption spectra of H-bonded complexes of HF from combined experimental studies and nonempirical calculations

The advantage of combining the spectroscopic experiments and nonempirical calculations in one study is discussed. Based on the results of earlier studies of H-bonded complexes H₂O⋯HF, dimethyl ether⋯HF, and acetone⋯HF and the study of HCN⋯HF performed in this paper, the requirements on the experimental conditions and theoretical approaches that can provide reliable spectroscopic data are generalized for the first time. Detailed recommendations on using the proposed theoretical method in multidimensional anharmonic calculations of other related AH⋯B complexes are also formulated. Comparative analysis of the data calculated for the four complexes shows for the first time that the intensity of shoulders of the ν₁(H–F) band (sum and difference transitions) is governed primarily by perturbations of the wave functions of low-frequency modes.     

Vibrational spectra and force constants of symmetric tops—XXII. Rotational analysis of ν2 + ν3 and ν1 + ν2 + ν3 of CF379Br and CF381Br

The rovibrational spectra of CF₃⁷⁹Br and CF₃⁸¹Br in the region of ν₂+ν₃ near 1120 cm⁻¹ and ν₁+ν₂+ν₃ near 2200 cm⁻¹ have been investigated with a resolution of 0.04 and 0.03 cm⁻¹ respectively. The rotational J structures have been resolved and were analyzed by means of polynomial and band contour simulation procedures. Molecular parameters (ν₀, x_ij, α^A,B) have been obtained from the analysis of the cold bands and the hot bands involving ν₆, 2ν₆, ν₃ and ν₅ for both isotopomers.     

Conformational analysis and interpretation of ν(OH) band in the IR spectrum of o-vinylphenol: a DFT study

Two-dimensional cyclic potential energy surface for internal rotation of vinyl and hydroxyl substituents in o-vinylphenol molecule was constructed by the B3LYP/6-311G(d) method. It was shown that o-vinylphenol molecule exists in the gas phase as a mixture of seven rotamers denoted as A (A′), B (B′), C (C′) and D. The B3LYP/cc-pVTZ calculated percentage of the rotamers A and A′ in which OH…π intramolecular interaction occurs, is at most 24%. The height of barriers t interconversions between o-vinylphenol rotamers varies from 0.1 to 5.2 kcal mol⁻¹. According to B3LYP/cc-pVTZ calculations, the inclusion of solvent effect in the framework of the polarizable continuum model for a solution of o-vinylphenol in CCl₄ leads to a decrease in theoretical values of ν(OH) frequencies by about 4–9 cm⁻¹ and to an increase in the percentage of the rotamers without intramolecular hydrogen bond by about 4.3% compared to the corresponding gas-phase values. The simulated IR spectral contours of ν(OH) bands are in good agreement with experimental one Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 499–508, March, 2008.     

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.     

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.     

Vibrational spectra in the ν(SiH) and ν(SiD) regions of chloro and bromodisilanes and ab initio geometry studies of C2H5Cl,Si2H5Cl and 1,1-Si2H4Cl2

Infrared measurements in the gas phase are reported for the ν(SiH) and ν(SiD) regions of Si₂H₅X, Si₂D₅X, 1,1-Si₂H₄X₂ and 1,1-Si₂D₄X₂ species where X = Cl, Br. Incomplete Raman data have also been obtained. All three possible isolated SiH stretching frequencies are observed in the spectra of the Si₂D₄X₂ samples, but only two from the Si₂D₅X ones. The missing ν^is(SiH) values are obtained by use of the frequency sum rule, and by harmonic local mode force field treatments of all the available ν(SiH) and ν(SiD) data, using a procedure previously tested on disilane.Ab initio calculations of the geometries of C₂H₅Cl, Si₂H₅Cl and 1,1-Si₂H₄Cl₂ using the 6-31G* basis set are reported. Trends in r_e(CH) or r_e(SiH) values reflect trends in ν^is(CH) or ν^is(SiH) ones. The alpha, trans and gauche effects of halogen are similar in CH and SiH compounds, although smaller in the latter. In both cases, ab initio calculations predict larger effects than are observed in the spectra, especially for the α effect of halogen.A kinetic isotope effect in the halogenation of disilane may occur. Reassignment of earlier spectra of disilyl iodide species is proposed.     

Infrared laser spectroscopy of the fundamental band of a 3π CO

Many rotational components of the fundamental band of metastable a ³Π CO have been measured in absorption using diode laser spectroscopy with concentration modulation detection. Line positions are in good agreement with predictions from optically derived parameters. Resolved or partially resolved splittings arising from lambda-doubling appear for the three Ω components. Splittings in the Ω = 1 and 2 spectra agree satisfactorily with molecular beam (rf) and microwave results while those in the Ω = 0 fundamental deviate by several linewidths (up to 0.015 cm-⁻¹) from calculated values.     

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.     

Solvent influence on infrared intensities of the ν(CO) band in ethyl acetate and fluroactetates

Infrared intensities of the ν(CO) stretching of R-COOC₂H₅, (R=-CH₃, -CH₂F, -CHF₂, -CF₃) were measured both in gas phase and solution in several solvents. Solvents differing in polarity and polarizability properties were chosen in order to study the influence of nonspecific solute-solvent interactions on the intensity value. Equations proposed by different authors were used to predict the value of gas phase intensity from those obtained in solution phase. Relations between intensity values in solution phase and empirical parameters of solvent polarity proved to be useful for the same purpose.