Combined analysis of microwave and infrared spectra of methyl iodide: rotational and l-type doubling constants of the v5, v3+v6 and v2 states

The rotational constant B and the l-type doubling constant q were determined for the v₅, v₃+v₆ and v₂, states of CH₂I from the microwave transition frequencies, in combination with the infrared data previously reported. Since these vibrational states were coupled through the Fermi resonance and the xy-type E-E and A₁-E Coriolis resonances, the analysis was made by setting up and solving the complete form of the secular determinants of the energy matrices. The rotational and l-type doubling constants were determined as B₅, = 0.250 173 cm^?1, B₃₆ = 0.247 600 cm^?1, B₂ = 0.249 369 cm^?1, q₅ = ?0.000 027 cm^?1 and q₃₆ = ?0.000 179 cm^?1, which are unperturbed by Fermi and Coriolis interactions. Other band constants for v₅ and v₃+v₆ were also refined in accordance with the new values of B₅ and B₃₆. The present study indicated that the combined analysis of microwave and infrared spectral data was useful for the precise determination of vibration-rotation, levels in the perturbed system.     

The calculation and accurate measurement of infrared band intensities: the v8 and v19 vibrations of monosubstituted benzenes

We report the results of calculations by the CNDO/2 molecular orbital method for the intensities of the v_19a and v_19b ring vibration of a series of mono-substituted benzenes and have repeated earlier calculations on the intensities of the corresponding v_8a and v_8b vibrations. These results are compared with intensity measurements in carbon tetrachloride solution made by improved techniques. Some gas phase measurements and results obtained for some deuterated compounds are included.     

Vibrational relaxation of CO2(v3) by O atoms

The vibrational relaxation time for CO₂(v₃) + O(³P) has been measured by laser fluorescence. The observed value, βCO₂.O = 0.21 ± 0.04 μsec, is an order of magnitude lower than the relaxation time for self-collisions.     

Inelastic neutron scattering spectra of alkali metal (Na,K) bifluorides: The harmonic overtone of v3

Inelastic neutron scattering spectra of MFHF (M  Na and K) have been measured up to energy transfers of ca. 4000 cm^?1 Both 0 → 1 and 0 → 2 transitions of the bending (v₂), and antisymmetric stretching (v₃) modes were observed. A normal harmonic (i.e. no quartic contribution) model for the dynamics of the bifluoride ion is entirely consistent with our observations. Evidence of phonon dispersion was observed in the band shape of v₃, but no structure attributable to the LO mode could be found. The similarity of the band shapes of v₃ for both NaFHF and KFHF is interpreted in terms of a very short range coupling mechanism.     

Fourier transform infrared spectroscopic analyses of the v12 fundamentals of C2H4 and C2D4

High-resolution infrared studies of isotopic ethylenes below 2000 cm^?1 have been commenced with a Nicolet FTIR spectrometer. Accurate vibration and rotation parameters for the v₁₂ fundamentals of C₂H₄ and C₂D₄ are determined from spectra recorded with 0.05 cm^?1 resolution. Excellent band contour simulations confirm that these bands are unperturbed throughout their range.     

The forbidden raman (v2, πu) transition in crystalline CS2

Raman spectra associated with the v₂(π_u) bending vibration of CS₂, which is forbidden for an isolated molecule, are presented The spectra are assigned to combination bands with phonons and show well-resolved critical point structure.     

The infrared spectrum and force field of the methyl-ammonium ion in (CH3NH3)2PtCl6

Infrared spectra of the CH₃NH₃⁺, CH₃ND₃⁺, CD₃NH₃⁺ and CD₃ND₃⁺ ions in bis(methylammonium)hexachloroplatinate(IV) have been recorded. The spectra are entirely consistent with the C_3v symmetry reported for the methylammonium ion, at temperatures between room temperature and 90 K. No spectral manifestations of the phase transition, which in (CH₃NH₃)₂PtCl₆ has been reported to take place at 125 K, were observed. Assignments of the infrared-active fundamentals have been made for each ion and a normal-coordinate analysis has been performed using the observed fundamental frequencies. Comparison with the infrared spectra of other methylammonium salts shows that hydrogen bonding in (CH₃NH₃)₂PtCl₆, if present, is weak.     

Dipole moment for the v2 = 1 vibrational state of 15NH3 by saturation laser stark spectroscopy

An intracavity Stark cell was used to observe inverse Lamb dips of five transitions of the ¹⁵NH₃v₂ band, saturated by CO₂ laser lines. Accurate values of the electric dipole moment of v₂ = 1, (J,K) = (4,4); (7,7); (8,8) and (11,9) states and of the (J,K) = (5,3) vibrational ground state have been obtained.     

Assignment of the microwave spectrum of trioxane in the v19(E) = v20E) = 1 state

An analysis of the rotational spectrum associated with two degenerate states simultaneously excited by one quantum is carried out for the first time for symmetric top molecules. The microwave spectrum of trioxane in the v₁₉(E) = v₂₀(E) = 1 state has been measured in the range 60–145 GHz and assigned using a graphical method. Accurate molecular parameters are determined by diagonalization of the energy matrices obtained by factoring the matrix constructed using the eigenvectors of the zeroth-order Hamiltonian as a basis.     

The Fermi doublet V2−V3 + V4 of CH3CN as a probe of molecular interactions

The Fermi doublet V₂?V₃ + V₄ of CH₃CN in basic, inert and acidic solvents has been studied by IR and Raman spectroscopy. The values of W, the Fermi coupling coefficient, obtained from IR spectra varies with the nature of the solvent while W evaluated from Raman data remains constant at 12.5 ± 0.5 cm^?1. The similar effects of Bronsted and Lewis acids on the band frequencies and intensities is evidence that the CN group complexes with acids via the N atom “n” electron pair and not the π bond.     

Electric dipole moment of Ph3 in the v4 = 1 state

The electric dipole moment of PH₃ in the v₄ = 1 state was measured by means of the Stark effect on the first two l-type doubling transitions     

The structure and energy of SiH+5. comparisons with CH+5 and BH5

Differences between SiH⁺₅ and CH⁺₅ are more significant than the similarities. The proton affinity of SiH₄ exceeds than of CH₄ by ≈25 kcal/mol. but the heat of hydrogenation of SiH⁺₃ is smaller than that of CH⁺₃ by nearly the same amount. Like CH⁺₅ the C₅ structures of SiH⁺₅ are preferred, but SiH⁺₅ is best regarded as a weaker SiH⁺₃—H₂ complex. D_3h, C_2v, and C_4v forms are much higher in energy and SiH⁺₅ should not undergo hydrogen scrambling (pseudorotation) readily, as does CH⁺₅ The neutral BH₅ is only weakly bound toward loss H₂, and the D_3h. C_2v, and C_4v forms are also high in energy. The contral-atom electronegativities, C⁺ > B > Si⁺, control this behavior. The electronegativities also determine the ability to bear positive charges. Thermodynamically. SiH⁺₅ and SiH⁺₃ are more stable than CH⁺₅ and CH⁺₃, respectively; hydride transfer occurs from SiH₄ to CH⁺₃ and proton transfer from CH⁺₅ to SiH₄.     

High-resolution infrared measurements of v1 and force field calculations for thioborine (HBS)

The gas-phase high-resolution spectrum is reported for v₁ of the linear molecule thioborine (HBS) from 2775 cm^?1 to 2720 cm^?1. Band centers and rotational constants are given for the 10⁰0-00⁰0 transitions of H¹¹B³²S, H¹⁰B³²S, H¹¹B³⁴S and H¹⁰B³⁴S and for the 11¹0-01¹0 transitions of H¹¹B³²S and H¹⁰B³²S. A valence force field is determined from measured values of v₁, D_o (the centrifugal distortion) and q (the l-doubling constant). The remaining unobserved vibrational fundamentals are calculated from the force constants.     

Collisional relaxation Of HF(v = 3,4) By HF,CH4 and CD4

Direct excitation of overtone vibrations in combination with near-infrared fluorescence detection provides collisional relaxation rate constants for HF(v = 3,4) by HF, CH₄ and CD₄. Observing fluorescence from a few rotational levels shows that the rotational manifold in HF(v = 4) equilibrates in about half the gas kinetic collision time.     

Vibrational energy exchange between CO(v=1) and 14N2 and CO(v=1) and 15N2XXXured to 60 k in the gas phase

Laser fluorescence technique has been used to measure (VV) exchange rates between CO(v = 1) and ¹⁴N₂ and ¹⁵N₂ XXX At 65 K exchange to ₁₅N₂ has 65 times the higher rate constant. Comparison with data for (VV) exchange in liquid ₂ shows that the isolated binary collision theory does not hold for the case of CO(v = 1) and ¹⁴N₂.     

Synthesis and characterization of ionic organotin compounds [R2SnCl2(2-quin)](HNEt3) and crystal structures of [(2,4-Cl2-C6H3CH2)2SnCl2(2-quin)](HNEt3)

Eight ionic organotin compounds [R₂SnCl₂(2-quin)]⁻(HNEt₃)⁺ have been synthesized by reactions of 2-quinH with R₂SnCl₂ (R = PhCH₂1, 2-Cl-C₆H₄CH₂2, 4-Cl-C₆H₄CH₂3, 2-F-C₆H₄CH₂4, 4-F-C₆H₄CH₂5, 4-CN-C₆H₄CH₂6, Ph 7, 2,4-Cl₂-C₆H₃CH₂8) in the presence of organic base NEt₃, and their structures have been characterized by elemental analysis, IR and multinuclear NMR (¹H, ¹³C, ¹¹⁹Sn) spectroscopies. The structure of [(2,4-Cl₂-C₆H₃CH₂)₂SnCl₂(2-quin)]⁻(NEt₃)⁺ (8) has been determined by X-ray diffraction study. Studies show that compound 8 has a monomeric structure with the central tin atom six-coordinate in a distorted octahedral configuration and the nitrogen atoms of the 2-quin ligands are coordinating to the tin atom in all the eight compounds.     

Effect of cation site-disorder on the structure and magneto-transport properties of Ln5/8M3/8MnO3 manganites

Five members of Ln_5/8M_3/8MnO₃ series with A-cation size variance (σ²) ranging between 3×10⁻⁴ and 71×10⁻⁴ Å², and the same A-cation size , have been synthesized by the ceramic method. The five manganites are single phase and they crystallize in the Pnma perovskite superstructure. The five compositions display ferromagnetic-paramagnetic transitions at temperatures ranging between 130 and 270 K, for the highest and lowest variance sample, respectively. The samples with smaller variances show sharp magnetization transitions and the samples with the larger variances display broad transitions. These transitions have also been studied by differential scanning calorimetry, DSC, and some enthalpy changes are reported. The resistivity study indicates that all samples display the expected metal-to-insulator transitions at temperatures ranging between 140 and 270 K. The samples have been analysed at room temperature by ultra-high-resolution synchrotron powder diffraction and the structural and microstructural features are reported. Furthermore, Nd_5/8Sr_0.255Ca_0.12MnO₃ () and Sm_0.225Nd_0.4Sr_0.308Ca_0.067MnO₃ () samples have also been studied by synchrotron powder diffraction at 140 K, below the transition temperatures. Both samples are found to be single phase above and below the transition by ultra-high-resolution synchrotron powder diffraction. The microstructure of the samples has been investigated through Williamson-Hall plots. Sample broadenings are markedly anisotropic and strongly dominated by microstrains with average values of the Δd/d term close to 14×10⁻⁴. A direct correlation is found between the microstrain values and the widths of the magnetization transitions.     

Three sandglass-type molybdophosphates obtained via a new route: Synthesis and characterization of X7[PMo8O30] (X=Na, K, NH4)

Three new polyoxometalates X₇[PMo₈O₃₀] (X=Na⁺, 1; K⁺, 2; NH₄⁺, 3) have been synthesized with the classical Keggin and/or Dawson heteropolymolybdophosphates and PCl₅ in acetonitrile-water solutions via hydrothermal treatment. The three compounds were characterized by different analyses including IR, ³¹P NMR spectroscopy, elemental analysis, electrochemistry, thermogravimetric analysis (TGA) and powder X-ray diffraction (XRD). Single crystal X-ray analyses were carried out on Na₇[PMo₈O₃₀] (1) and (NH₄)₇[PMo₈O₃₀] (3). Compound 1 and 3 crystallize in the orthorhombic system. The structure of compound 2 was confirmed by the IR spectra and powder XRD. All the three compounds contain the same octamolybdophosphate polyoxoanion [PMo₈O₃₀]⁷⁻, which consists of two Mo₄O₁₅ moieties linked by one central PO₄ tetrahedron, leading to a remarkable sandglass-like structure.     

Synthesis and crystal structure of new uranyl tungstates M2(UO2)(W2O8) (M=Na, K), M2(UO2)2(WO5)O (M=K, Rb), and Na10(UO2)8(W5O20)O8

The solid-state reactions of UO₃ and WO₃ with M₂CO₃ (M=Na, K, Rb) at 650°C for 5 days result, accordingly the starting stoichiometry, in the formation of M₂(UO₂)(W₂O₈) (M=Na (1), K (2)), M₂(UO₂)₂(WO₅)O (M=K (3), Rb (4)), and Na₁₀(UO₂)₈(W₅O₂₀)O₈ (5). The crystal structures of compounds 2, 3, 4, and 5 have been determined by single-crystal X-ray diffraction using Mo(Kα) radiation and a charge-coupled device detector. The crystal structures were solved by direct methods and Fourier difference techniques, and refined by a least-squares method on the basis of F² for all unique reflections. For (1), unit-cell parameters were determined from powder X-ray diffraction data. Crystallographic data: 1, monoclinic, a=12.736(4) Å, b=7.531(3) Å, c=8.493(3) Å, β=93.96(2)°, ρ_cal=6.62(2) g/cm³, ρ_mes=6.64(1) g/cm³, Z=4; 2, orthorhombic, space group Pmcn, a=7.5884(16) Å, b=8.6157(18) Å, c=13.946(3) Å, ρ_cal=6.15(2) g/cm³, ρ_mes=6.22(1) g/cm³, Z=8, R1=0.029 for 80 parameters with 1069 independent reflections; 3, monoclinic, space group P2₁/n, a=8.083(4) Å, b=28.724(5) Å, c=9.012(4) Å, β=102.14(1)°, ρ_cal=5.83(2) g/cm³, ρ_mes=5.90(2) g/cm³, Z=8, R1=0.037 for 171 parameters with 1471 reflections; 4, monoclinic, space group P2₁/n, a=8.234(1) Å, b=28.740(3) Å, c=9.378(1) Å, β=104.59(1)°, ρ_cal=6.13(2) g/cm³,  g/cm³, Z=8, R1=0.037 for 171 parameters with 1452 reflections; 5, monoclinic, space group C2/c, a=24.359(5) Å, b=23.506(5) Å, c=6.8068(14) Å, β=94.85(3)°, ρ_cal=6.42(2) g/cm³,  g/cm³, Z=8, R1=0.036 for 306 parameters with 5190 independent reflections. The crystal structure of 2 contains linear one-dimensional chains formed from edge-sharing UO₇ pentagonal bipyramids connected by two octahedra wide (W₂O₈) ribbons formed from two edge-sharing WO₆ octahedra connected together by corners. This arrangement leads to [UW₂O₁₀]²⁻ corrugated layers parallel to (001). Owing to the unit-cell parameters, compound 1 probably contains similar sheets parallel to (100). Compounds 3 and 4 are isostructural and the structure consists of bi-dimensional networks built from the edge- and corner-sharing UO₇ pentagonal bipyramids. This arrangement creates square sites occupied by W atoms, a fifth oxygen atom completes the coordination of W atoms to form WO₅ distorted square pyramids. The interspaces between the resulting [U₂WO₁₀]²⁻ layers parallel to plane are occupied by K or Rb atoms. The crystal structure of compound 5 is particularly original. It is based upon layers formed from UO₇ pentagonal bipyramids and two edge-shared octahedra units, W₂O₁₀, by the sharing of edges and corners. Two successive layers stacked along the [100] direction are pillared by WO₄ tetrahedra resulting in sheets of double layers. The sheets are separated by Na⁺ ions. The other Na⁺ ions occupy the rectangular tunnels created within the sheets. In fact complex anions W₅O₂₀¹⁰⁻ are built by the sharing of the four corners of a WO₄ tetrahedron with two W₂O₁₀ dimmers, so, the formula of compound 5 can be written Na₁₀(UO₂)₈(W₅O₂₀)O₈.     

35Cl Nqr spectroscopy of the [PO2Cl2]− and POCl3 groups in Me(PO2Cl2)2·2D (Me = Mg,Ca, Mn; D = POCl3,CH3COOC2H5,CH3COCH3)

³⁵Cl NQR spectra of dichlorophosphates Me(PO₂Cl₂)₂ · 2D (Me = Mg, Ca, Mn; D = CH₃COOC₂H₅, CH₃COCH₃, POCl₃) are studied in the temperature range 77 ? T (K) ? 305. It is shown that the three compounds with CH₃COOC₂H₅ as donor are isomorphic at 77 K, the crystal structure of Mn(PO₂Cl₂)₂· 2CH₃COOC₂H₅. The structure of Mg(PO₂Cl₂)_2^?· 2CH₃COCH₃ and of Mg(PO₂Cl₂)₂ · 2POCl₃ probably consists of infinite chains as found for Mn(PO₂Cl₂)₂· 2CH₃COOC₂H₅. Mg(PO₂Cl₂)₂· 2CH₃COOC₂H₅ shows phase transformations and a complicated dynamical behaviour leading to strong deviations from a Bayertype NQR function v = f(T). The donor capacity of POCl₃ in Mg(PO₂Cl₂)₂· 2POCl₃ is comparable with the donor strength in AsCl₃ · POCl₃ · A d_π-p_π overlap of the P-O bond influences the P-Cl bond.