Light-induced isomerization and photochemical transformation of methylformate in an argon matrix. Vibrational frequencies,force field,and normal coordinate analysis of trans-methylformate

When methylformate (HCOOCH₃), isolated in an argon matrix, is excited into the $\text{S}{}_1\text{(ππ}{}^1\text{) ← S}{}_0$ transition at 248 nm the prevailing cis conformer is transformed into the trans conformer. In a consecutive photolysis step the latter is decomposed to stable products including a hydrogen-bonded (1:1) complex between CO and methanol, acetic acid, and CO₂ and methane. The efficient photolytic preparation of the unstable trans-methylformate and its deuterated analogs DCOOCH₃, HCOOCD₃, and DCOOCD₃ in an argon matrix allowed measurement of their ir spectra (170–4000 cm^?1) in great detail thus providing an almost complete set of fundamentals together with a number of combination and overtone frequencies. With a normal coordinate analysis based on a constrained valence force field (transferable valence force field approach) the frequencies of trans-methylformate were assigned and compared to those of the remeasured cis rotamer.     

Relative Cl 2p:P 2s photoionization intensities in transition metal complexes

X-ray photoelectron spectra of the Cl 2p_{$\text{1}\text{2}$, $\text{3}\text{2}$}, P 2s region were obtained for nine transition metal complexes. The Cl:P atom ratios ranged from 1:3 to 3:2 and exhibited a linear relationship with the Cl 2p_{$\text{1}\text{2}$, $\text{3}\text{2}$} : P 2s intensities. Using AlKα radiation, the ratio of the Cl 2p: P 2s photoionization intensities was found to be 2.5: 1.0 with the McPherson ESCA-36 Photoelectron Spectrometer operated in its standard configuration.     

The identification of two entrance channels in the reaction of metastable helium He(23S,21S) with SO2

The energy spectrum of electrons emitted in the reaction of He(2³S) and He(2¹S) with SO₂ indicates that in addition to the covalent entrance channel a strongly attractive ionic channel plays a role. We find upper limits for the well depth of the potential curve that corresponds to the latter channel of D_e ? 3.5 eV and D_e ? 4.3 eV for He(2³S) and He(2¹S) as the reaction partner, respectively. The partitioning between the two entrance channels can be understood by assuming the coupling matrix between both channels to depend strongly on the orientation of the SO₂ molecule with respect to the incident metastable He*.     

Vibrational spectra of Matrix isolated binary and mixed cadmium dihalides

The Raman spectra CdX₂ and CdXY (X, Y = Cl, Br, I) molecules isolated in solid krypton at 20°K are reported together with the matrix isolation infrared spectrum of CdX₂ and CdXY (X, Y = Br, I) molecules. Isotopic effects and force constants are discussed and several irregularities in them are interpreted as possible indications of slightly bent structures. The bending vibration frequency of CdClI as well as several bands assigned to dimers are also reported.     

Relation between electrooptical constants and polar tensors of CH3F,CD3F,CH3Cl,CD3Cl,CH3Br,CD3Br,CD3I,and CD3I

Infrared intensity analysis was done in two ways. In one approach, formulas connecting electrooptical parameters (eop's) and intensities were derived and, using the intensities, the former were obtained. In evaluating the eop's the intensity sum equations were used directly so that the sign ambiguity of $\text{δP}\text{δQ}$ is avoided. In the other method, polar tensors were obtained directly from intensities. The two methods have now been connected, and polar tensors have been obtained in terms of electrooptical parameters so that the former were also free from sign ambiguity of $\text{δP}\text{δQ}$. They compare well with those obtained directly from intensities. In similar connecting formulas by other authors [see, for example, P. L. Prasad, J. Chem. Phys., 69, 4403, (1978)], both polar tensors and eop's were affected by the sign ambiguity.     

Single orbital relaxations accompanying core ionization in the isoelectronic series CH4, NH3, H2O,HF and Ne

Single orbital contributions to the total relaxation energy accompanying core ionization are computed by means of non-empirical LCAO MO SCF calculations within the ΔSCF formalism for the isoelectronic series CH₄, NH₃, H₂O, HF and Ne. Individual contributions to the total relaxation energy associated with the valence levels of essentially core-like 2s character are also presented.     

Penning ionization electron spectroscopy of H2O,D2O,H2S and SO2

Electron energy peak shifts and peak shapes were determined in the ionization of H₂O, D₂O, H₂S and SO₂ by Ne(³P₂) and He(2¹S, 2³S) metastable atoms. The shifts are large, especially in ionization of H₂O and D₂O into the ionic ground state and are probably mostly due to chemical interaction during the collision.In a previous paper the electron energy distribution curves for ionization of CO, HCl, HBr, N₂O, NO₂, CO₂, COS and CS₂ by helium, neon and argon metastables and the characteristics of this ionization were described¹. In this paper the series of triatomic molecules was extended to the molecules H₂O, D₂O, H₂S and SO₂. Because all these molecules have considerable dipole moments it could be expected that the peak shifts might be enhanced as compared with other triatomic molecules.     

Emission spectra of polyatomic radical cations in the gas phase: Ã2Πu → X̃2Πg band systems of Cl(CC)2 Cl+, Br(

Emission spectra of the dihalodiacetylene radical cations, X(CC)₂X⁺ with X = Cl, Br and I, excited in the gaseous phase by low energy e     

Field ion and field desorption mass spectrometry of inorganic compounds

The review on recent developments in field ionization mass spectrometry of inorganic compounds concerns the different mechanisms of ion formation at surfaces and under the influence of extremely high electric fields, field dependent chemical reactivity at surfaces and ion desorption from surfaces for mass spectrometric analysis. Applications in various areas are discussed, where this method has been used to identify surface compounds or to study kinetic phenomena at interfaces.     

Self-consistent calculations of the density of 2D electron gas in AlxGa1−xAsGaAs heterointerface as a function of the doping level in n-AlxGa1−xAs layer

Sheet density of two-dimensional electron gas at the Al_xGa_1?xAs heterointerface is calculated self-consistently as a function of doping level in n-Al_xGa_1?xAs layer by taking into account shallow donor level and the DX centers. The results show a good agreement with the experimental results reported by Ishikawa et al. Dingle's rule of the conduction band discontinuity does not agree with the present results but with 0.62 rule proposed recently by Watanabe et al.     

Interlayer force constants in high symmetry layer crystals

Symmetry adapted linear chain model has been used for the evaluation of compressional and shear interlayer force constants in MnCl₂ and GaSe from the observed zone centre and zone edge frequencies. The method is applicable to two major groups of high symmetry layer crystals having XAX and XAAX type layers.     

The preparation and characterization of the cobalt skutterudites CoP3, CoAs3 and CoSb3

Single crystals of the cobalt skutterudites CoP₃, CoAs₃ and CoSb₃ have been prepared by the chemical vapor transport technique using chlorine as the transport agent. Chemical analysis and density measurements were used to determine accurately the stoichiometry of these crystals. Physical properties of chemically pure single crystals were obtained by X-ray diffraction, magnetic susceptibility and electrical measurements. CoP₃ is a diamagnetic semiconductor with an optical band gap of 0.45 eV. CoAs₃ and CoSb₃ are also diamagnetic and show an increase in their resistivity as a function of increasing temperature. In addition, they do not give any measurable absorption edge but absorb radiation at all frequencies from 0.4 to 4.3 eV.     

X-ray photoelectron spectroscopy of TiO2 and other titanate electrodes and various standard Titanium oxide materials: Surface compositional changes of the TiO2 electrode during photoelectrolysis

Surface compositional changes were observed for TiO₂ single crystal electrodes used for photoelectrolysis of water. Surface stoichiometries of several types of TiO₂, SrTiO₃ and BaTiO₃ electrodes were characterized by XPS and compared with a variety of titanium, titanium oxide and titanium hydride standard materials. Reduction of the electrode surface in a hydrogen atmosphere results in an oxygen deficient surface composition. Photoelectrolysis at current densities of $\text{10–15}\text{mA}\text{cm}{}^2$ for periods up to 8 h appears to return the electrode surface to a nearly stoichiometric oxygen-to-metal ratio. Reduction of the titanium oxide surfaces was also observed by exposure to an argon ion beam. Analysis of the electrode surface by a combination of XPS and ion-sputter profiling was still possible by simultaneous analysis of standard materials.     

Chemical diffusivity of lithium in LiyTi1+xS2

Chemical diffusivity of lithium was measured in polycrystalline Li_yTi_1+xS₂ using current—pulse relaxation technique on Li/1M LiC1O₄ in THF/Ti_1+xS₂ cell. Excess titanium of the nonstoichiometric titanium disulfide did not so much reduce the lithium diffusivity in the interlayer region as in the case of sodium. The diffusivity varied with the amount of intercalated lithium. It had a maximum value of 5 × 10^?8cm²/s for all compounds of Ti_1+xS₂ (0?x?0.13) when the calculations were based on the geometrical surface area. It was calculated as about 3 × 10^?10cm²/s using the effective surface area.     

Intramolecular coupling of vibrational modes and the assignments of the partially deuterated dihalogenomethanes, -silanes, and -germanes

The fundamental vibrational wavenumbers of seven molecules of the type MHDX₂ (where M = C, Si, Ge and X = F, Cl, Br) have been calculated from those of the corresponding species MH₂X₂ and MD₂X₂, using the complete isotopic rule of Brodersen and Langseth. These wave-numbers have been used to test the force fields previously computed for the MH₂X₂ and MD₂X₂ molecules. The potential energy distributions calculated for the MHDX₂ species have been employed as aids in clarifying the assignments of their vibrational spectra.     

The crystallographic shear planes of the non-stoichiometric molybdenum oxides as revealed by RHEED: Investigation from the Mo18O52(100) surface

Large Mo₁₈O₅₂ crystals are obtained by an appropriate crystallization method. The examination of their well developed surfaces by the use of reflection high energy electron diffraction (RHEED) proves that these are (100) surfaces stepped along [010] directions. It is concluded that this oxide surface conformation can be connected to the particular Mo₁₈O₅₂ structure which is built up of MoO₃ slabs of finite width mutually joined by crystallographic shear planes (CS planes). Transmission electron microscopy (TEM) analysis from Mo₁₈O₅₂ crystal flakes confirms that these are single crystals without disorder in the periodicity of the CS planes.     

Magnetic properties of the rare-earth diborodicarbides (RB2C2)

The magnetic susceptibility of RB₂C₂ has been measured in the temperature range of 3–300 K. Curie-Weiss fits to the susceptibilities led to effective moments in agreement with those expected for R³⁺ ions. The RB₂C₂ (R = Ce, Nd, Sm, Gd, Tb, Er, and Tm) compounds are antiferromagnetic. Metamagnetic transitions at low fields were observed for CeB₂C₂ and TbB₂C₂. The compounds, DyB₂C₂ and HoB₂C₂, are ferromagnets with complex magnetic structures. Praseodymium borocarbide becomes a Van Vleck paramagnet at low temperature. The magnetic ordering temperatures of these compounds are discussed in terms of their crystal structure and the RKKY theory.     

The ν2 band of 14NH3: A calibration standard with better than 1 × 10−4 cm−1 precision

The Fourier transform spectra and the diode laser spectra of the ν₂ band of ¹⁴NH₃ have been measured with 0.005 and 0.002 cm^?1 resolution, respectively. A simultaneous least squares analysis has been carried out of these data together with the microwave, submillimeterwave, diode-laser heterodyne, and infrared-microwave two-photon transition frequencies between the ground and the ν₂ inversion-rotation levels. A theory of the Δk = ±3n interactions in the ground and ν₂ excited states of ammonia (?. Urban, V. ?pirko, D. Papou?ek, J. Kauppinen, S.P. Belov, L. I. Gershtein, and A. F. Krupnov, J. Mol. Spectrosc.84, 288–304 (1981)) has been used in the analysis. The “smoothed” values of the ν₂ band wavenumbers can be used for calibration purposes with better than 1 × 10^?4 cm^?1 precision. On the basis of these results, a critical evaluation has been carried out of several experimental techniques of very high resolution infrared spectroscopy.     

Surface characterization and catalytic CO + H2 reaction on Fe82.2B17.8 amorphous alloy

Fe_82.2B_17.8 amorphous ribbon has been used as a catalyst for the Fischer-Tropsch-type reaction of CO+H₂. Specific activity has been found to be at least an order of magnitude higher than that of either the crystallized ribbon of identical composition or the supported iron catalyst. Before and after the catalytic tests the ribbons were characterized by XRD, XPS, UPS and Mössbauer spectroscopy in transmission and in conversion electron modes. Conversion electron Mössbauer spectroscopy and UPS proved that the surface of the amorphous ribbons is being partially crystallized during 8000 min reaction time at a maximum reaction temperature of 560 K. The superior catalytic activity has been explained by stabilization of the small iron particles and Fe₂O₃ by boron atoms at the surface and by suppressed carbide formation.     

Investigation of H+ motion in the 21-hydrates of 12-tungstophosphoric and 12-molybdophosphoric acids by ac conductivity and pulsed 1H NMR measurements

AC conductivity and ¹H NMR relaxation time measurements are reported for the heteropolyacids H₃PM₁₂O₄₀. 21H₂O (M = W, Mo) over a range of tempereatures.Ambient temperature proton conductivites are ? 1 S m^-1, with conductivity activation energies E ? 40 kJ mol^-1.The NMR results are interpreted in terms of a range of motional processes leading to distributions of translational correlation times. The behaviour is compared to motions in zeolites and of water sorbed by charcoal.