Effect of the internal rotation of the CHD2 group on the CH stretching infrared and Raman spectra of toluene C6D5CHD2 and nitromethane NO2CHD2 in vapor phase

Gas-phase infrared and Raman spectra of toluene C₆D₅CHD₂ and nitromethane NO₂CHD₂ were recorded in the CH stretching region. They are all characterized by a strong band with a weaker one at lower frequency. These bands have simple Raman profiles and their infrared contours are respectively of A and C type. A quantum theory of these spectra is put forward, assuming an anharmonic coupling of the νCH mode with the internal rotation of the CHD₂ group in the adiabatic approximation. Theoretical calculations based on this model give a good fit of the experimental Raman bandshapes and a good picture of the observed infrared spectra. Thus each of the observed bands can be characterized. The frequency of the intense band is the average of that of the νCH mode during the almost free internal rotation of the CHD₂ group, while the frequency of the weaker band is approximately equal to the minimal νCH frequency. This last one corresponds to the position of the CH bond in a plane perpendicular to that of the molecule (ν_⊥CH). The frequency difference between ν_∥CH (the CH bond being in the plane of the molecule) and ν_⊥CH is found to be 42 cm^?1 for the two compounds.     

Supertransferred hyperfine structure in EPR of V4+ ion in Ca3In2Ge3O12 garnet

Interaction of an unpaired electron of the tetrahedral V⁴⁺ ion in Ca₃In₂Ge₃O₁₂ garnet with the four nearest In nuclei gives rise to clearly resolved structure of EPR spectra. We report the observation and analysis of these spectra at three frequencies and at temperature 77 K. The temperature dependence between liquid helium and the room temperatures was also studied. Parameters of the spin Hamiltonian are g_∥=1·8735; g_⊥=1·9825; ∣ ¦A∥|=150·4×10^?4cm^?1; ¦ A_⊥¦ = 36·7 × 10^?4 cm^?1. The supertransferred hyperfine interaction was found to be isotropic, absolute value of the corresponding parameter a is 22·1 × 10^?4 cm^?1.     

Analysis of the ν2 and ν4 infrared bands of CD4

The infrared spectrum of totally deuterated methane CD₄ has been recorded between 930 cm^?1 and 1180 cm^?1 under high resolution (0.003 cm^?1). The ν₂ and ν₄ bands of ¹²CD₄ have been reanalyzed on the basis of a complete third-order Hamiltonian including all the coupling terms linking the upper states of the two bands. A set of only 16 self-consistent parameters have been adjusted to fit more than 1650 assigned transitions reaching a maximum upper state J value of 20. The obtained standard deviation is 0.0041 cm^?1. In addition, 171 lines of the ν₄ band of ¹³CD₄ have been assigned. They have been analyzed, in the same dyad scheme, by adjusting 7 parameters of the ν₄ band together with the main ζ₂₄ Coriolis parameter. The obtained standard deviation is only 0.0012 cm^?1.     

High resolution Fourier transform infrared spectroscopy on CH2DI and CHD2I: evaluation of the ground state constants and analyses of the C-I stretching bands ν3

Abstract

The high resolution (0.0010cm^?1) Fourier transform infrared spectra of the partially deuterated methyl iodide molecules CH₂DI and CHD₂1 have been recorded and analysed in the ν₃ band regions around 510cm^?1. The fundamental band ν₃ is associated with the stretching of the C-I bond and the spectra appear therefore as an asymmetric rotor hybrid a/b-type band and hybrid a/c-type band for CH₂DI and CHD₂I, respectively. About 4700 transitions in the case of CH₂DI and about 3900 transitions in the case of CHD₂I have been assigned. The ground state rotational constants of CH₂DI and CHD₂I have been obtained using the ground state combination differences calculated from the assigned ν₃ transitions and 16 microwave transitions from literature. The S reduced Watson's Hamiltonian has been used in the calculations. In addition, the upper state parameters describing the v₃=1 vibrational states of these molecules have been determined. The obtained ground state constants as well as the upper state parameters have been compared to the corresponding constants of the symmetric top species CH₃I and CD₃I     

Diode laser spectra of the ν2 band of 14N16O2: The (010) state of NO2

Diode laser spectra of the ν₂ band of NO₂ are recorded and analyzed. Due to the very high resolution (0.002 cm^?1), the Q branches are completely resolved. Although the whole ν₂ band is not completely covered, the quality of the spectra led to an improved set of rotational and spin-rotation constants. The band center is found to be ν₂ = 749.6541 ± 0.0012 cm^?1.     

Stark spectroscopy with the CO2 laser: The ν5 band of 12CD3F

The ν₅ band of ¹²CD₃F was studied using coincidences with the 9.4-μm band of the ¹²C¹⁶O₂ laser and the 9.25-μm band of the ¹²C¹⁸O₂ laser. The resonances were analyzed together with the infrared spectra and recent microwave results to give the following vibration-rotation parameters and dipole moment in the ν₅ state: ν₀ = 1072.35093 (11) cm^?1; B = 0.681137 (4) cm^?1; A₅-A₀ = ?0.01437 (3) cm^?1; Aζ_z = ?0.81453 (3) cm^?1; μ_ν5 = 1.8751 (25) D. The parameters should be useful in assigning some near millimeter laser lines in CD₃F.     

Optical and ESR spectra of the C4H radical in rare gas matrices at 4 K

C₄H (butadinyl) was trapped in Ar and Ne matrices at 4 K by the uv photolysis of a mixture of C₄H₂ and the rare gas. CC stretching and CH bending modes have been identified in the ir at 2060 and 735 cm^?1. A band system appearing in the 2500–3000 Å region with (0, 0) at 33 800 cm^?1 has been analyzed and tentatively assigned to a ²Π_r ← X²Σ transition. C₄D: Ar spectra confirm the optical assignments. The ESR spectrum exhibits a proton hyperfine splitting b = A_⊥(H) = 16.5 MHz, at g_⊥ = 2.0004(5). The spin-doubling constant, γ, is estimated to be +0.0006(2) cm^?1.     

Vibration-rotation spectra of CH3CN: The ν7 band and its hot bands near 1040 cm−1

Infrared spectra of CH₃CN were measured in the range 170–600 cm^?1 with a Fourier transform spectrometer (0.06 cm^?1 resolution) and several small portions in the range 1020–1065 cm^?1 with a tunable Pb_1?xSn_xTe diode laser spectrometer (0.001 cm^?1 resolution). The ν₇ band was analyzed by taking account of local Fermi resonance with 3ν₈¹, and the following parameters were determined: ν₇ = 1041.8446(15) cm^?1; 3ν₈¹ =1077.88(5) cm^?1; and ∥k₇₈₈₈∥ = 1.98(1) cm^?1. Two hot bands in the ν₇ band region, i.e., (ν₇ + ν₈)² ? ν₈¹ and ν₆¹ ? ν₈¹, were also analyzed, and ν₈ = 365.05(5) cm^?1 and ζ₈ = 0.874(1) were determined by use of the observed transitions of the ν₇ + ν₈ and ν₆ bands.     

The Coriolis interaction between the fundamentals ν2 and ν5 of CD3Br

The bands ν₂ and ν₅ of CD₃Br have been measured at a resolution of 0.010 cm^?1. They were analyzed simultaneously by taking into account the xy-Coriolis interaction. More than 1600 transitions were assigned for each isotopic species CD₃⁷⁹Br and CD₃⁸¹Br. The Coriolis coupling term proved to be ζ_2,5^y = 0.559. The band centers are (in cm^?1) ν₂: 991.401 (CD₃⁷⁹Br), 991.390 (CD₃⁸¹Br); ν₅: 1055.474 (CD₃⁷⁹Br), 1055.471 (CD₃⁸¹Br).     

Infrared diode laser spectroscopy of FCO: The ν1 and ν2 bands

The ν₁ (CO stretching) and ν₂ (CF stretching) bands of the FCO radical were observed with Doppler-limited resolution by an infrared diode laser spectrometer with Zeeman and source modulation. The FCO radical was generated by a 60-Hz discharge in one of the following three gas mixtures: O₂ + C₂F₄, CO + SF₆, and CO + C₂F₄, all diluted with He. The observed spectra were analyzed to determine the rotational constants, the centrifugal distortion constants, and the spin-rotation interaction constants. The band origins, 1861.6372(1) and 1026.1283(1) cm^?1 [with standard errors in parentheses], which were obtained, were found to agree well with matrix data, 1857 and 1023 cm^?1, respectively. The assignment of the observed spectra to the FCO radical was further supported by observing the ν₁ band of F¹³CO, which was obtained from ¹³CO and SF₆. The molecular structure and the force field of FCO are briefly discussed by using molecular constants obtained from the observed spectra.     

Movements of matrix-isolated methyl fluoride and isotopic species studied by infrared absorption spectroscopy

Infrared absorption spectra were recorded in the 10-μm region for the three isotopic methyl fluoride molecules ¹²CH₃F, ¹²CD₃F, ¹³CD₃F, in the four rare gas matrices and in nitrogen. The two lowest fundamental modes ν₃ (CF stretching) and ν₆ (bending) have been systematically studied, as well as the ν₂ and ν₅ modes of ¹²CD₃F. Relative intensity measurements show that the weak ν₆ transition is enhanced by the matrix, compared to its gas-phase value. Frequency measurements yield vibrational shifts which can be compared to a theoretical estimate of the ν₃ shift based on the Lennard-Jones-Devonshire cell model. These molecules are almost freely rotating in the matrices and a rotational analysis in the ν₃ region brings out quantitative values of the barrier to free rotation as defined in Devonshire's theory. Frequency and relative intensity measurements are also reported for dimeric species.     

The ν4 and ν2 Raman bands of CHD3

The CHD₃ Raman spectrum from 1925 to 2455 cm^?1 has been photographed with a resolution of about 0.2 cm^?1, showing the overlapping ν₂ and ν₄ bands. Ground state combination differences yield C₀ = 2.6297 ± 0.0003 cm^?1. The ν₄ state is weakly perturbed, but reasonably accurate values could be obtained for ν₄ = 2250.88 ± 0.10 cm^?1, (Cζ)₄ = 0.656 ± 0.010 cm^?1, C₄ - C₀ and B₄ - B₀. Some of these constants differ significantly from values previously estimated by infrared workers. For the ν₂ state the constants determined are in good agreement with recent infrared results.     

Barrier to internal rotation of the silyl group in cyclopropylsilane from combination band spectra

Combination band spectra arising in the region 2000–2300 cm^?1 of cyclopropylsilane can be attributed to the sum and difference bands of the internal rotation with an SiH stretching mode. Analysis of these spectra leads to a potential function for the internal rotation V(cm^?1) = 693.92(1 ? cos 3φ) ? 10.28(1 ? cos 6φ), where φ is the angle of internal rotation. The barrier to internal rotation is thus 1.98 kcal/mole.     

The high-resolution infrared spectrum of ethane-1,1,1-D3 rovibration analyses of the pseudoperpendicular A1A2ν9 + ν10 band and the parallel ν3 + ν4 and ν5 bands

A complete vibration-rotation analysis was made of the A₁A₂ combination band ν₉ + ν₁₀ of CH₃CD₃ at 2582 cm^?1. This band exhibits pseudoperpendicular structure due to the large effective Coriolis interaction constant (ζ ≈ 0.7), which couples the almost degenerate A₁ and A₂ vibrational components for all nonzero values of the rotational quantum number K, and gives a subband Q-branch spacing of 2.5 cm^?1. The location of the band center is assisted through an interruption of the perpendicular-like structure, since both K = 0 Q branches are forbidden by the vibrational and rotational selection rules. The conventional A₁ parallel bands ν₃ + ν₄ at 2507 cm^?1 and ν₅ (CC stretch) at 905 cm^?1 were also analyzed. For ν₅, a combination of numerical analysis and band contour simulation was used to determine a set of upper-state rotation parameters. Combination of the present results with previous data for ν₉ and 2ν₃ permits rotational parameters to be derived for the ν₄ and ν₁₀ fundamentals of CH₃CD₃. Neither of these fundamentals are amenable to straightforward analysis, both being very weak in the infrared and overlaid by the intense ν₁₁ fundamental.     

The ν3 band of CD3I around 500 cm−1

The region of the lowest fundamental band ν₃ of CD₃I around 500 cm^?1 is studied at a resolution of 0.015 cm^?1. The K structure in the parallel band ν₃ is resolved for K = 6 – 14. Molecular constants for the ν₃ level are derived, including α₃^A = 3.055(13) × 10^?3 cm^?1. The “hot” band 2ν₃-ν₃ is also investigated.     

Tunable laser diode study of the ν3 band of SiF4 near 9.7 μm

Doppler-limited tunable-diode laser spectra of the stretching fundamental ν₃ of ²⁸SiF₄ near 1031 cm^?1 were analyzed and the spectroscopic constants determined. The ν₃ vibrational dipole moment derivative was determined for several rovibrational lines.     

Microwave spectrum of methylene fluoride-d2, CD2F2 in the excited vibrational states

The rotational spectra of ¹²CD₂F₂ in the ν₂, ν₃, ν₄, 2ν₄, ν₅, ν₇, ν₈, and ν₉ states were observed and assigned. Weak Coriolis interactions between ν₃ and ν₇, ν₃ and ν₉, and ν₅ and ν₇ were analyzed using approximate expressions for the rotational energy levels. The resonance between the ν₂ and the ν₈ state was found much stronger, and an effective two-dimensional Hamiltonian with the Coriolis term in the off-diagonal block was set up to analyze the spectra. The effect of the Fermi resonance between ν₃ and 2ν₄ was found to be very small.The ground-state spectrum of ¹³CD₂F₂ was observed and the rotational constants and the centrifugal distortion constants were determined. The data on ¹²CD₂F₂ and ¹²CDHF₂ were also improved very much in accuracy.The Coriolis coupling constants and the differences between two vibrational levels in resonance, which were determined by the analysis of the satellite spectra, are in good agreement with those obtained from vibrational spectra, except for the ν₂ band center, which is revised to 1170.3 cm^?1. The force constants were also checked using the centrifugal distortion constants of ¹²CD₂F₂, ¹³CD₂F₂, and ¹²CHDF₂.     

Vibrational spectra and force constants of symmetric tops: ν1, ν5, and 2ν5 of CF335Cl and CF337Cl

The gas phase infrared spectra of CF₃³⁵Cl and CF₃³⁷Cl have been recorded in the ν₁ region and 2ν₅ regions with a resolution of 0.09 cm^?1. Additionally the ν₅ fundamental of CF₃Cl, with natural isotopic abundance, has been reinvestigated with a resolution of approximately 0.36 cm^?1. Molecular constants have been evaluated from the observed spectra by means of polynomials and band contour simulation. The possibility of a Fermi resonance between ν₁ and 2ν₅ is discussed.     

An X-Y Coriolis perturbation in ν4 of CD3Br

The region 2242–2273 cm^?1 of the ν₄ band in CD₃Br was remeasured at a resolution limit of 0.025 cm^?1. Line assignments were extended up to J = 50 in some subbands. Transitions in the KΔK = ?8 subband were assigned, and the perturbation apparent in this region was attributed to the x-y Coriolis interaction with ν₃ + ν₅^±1 + ν₆^±1. The x-y Coriolis coupling parameter W_xu and the ν₃ + ν₅^±1 + ν₆^±1 band center (in cm^?1) are 0.01960 and 2339.17 for CD₃⁷⁹Br, while the corresponding values for CD₃⁸¹Br are 0.01956 and 2337.95.     

Far-infrared internal rotation spectrum of CH3OD and CD3OD

The far-infrared spectra of the Q branches of hindered rotation in CH₃OD and CD₃OD have been investigated in the 80- to 250-cm^?1 spectral region. The theoretical spectra are calculated using the full set of Kirtman constants and are compared with the experimental spectra of resolutions up to 0.13 cm^?1.