Theoretical absolute J-manifold intensities of the ν3 fundamental of GeH4

Theoretical absolute integrated of the J-manifolds P(1)-P(20), R(0)-R(20), and the central Q-branch in the ν₃ fundamental of GeH₄ have been projected from experimental intensity measurements. Values are presented in tabular form as a function of temperature from 200 to 340°K in 20°K increments.     

The ground-state rotational constants of germane

The ground-state rotational constants B₀, D₀, and H₀ have been determined for GeH₄ from the analysis of ground-state combination differences in the infrared spectra of isotopically enriched ⁷⁰GeH₄, ⁷²GeH₄, and ⁷⁴GeH₄. The spectra were recorded at 0.06-cm^?1 resolution and about 0.005-cm^?1 precision for unblended lines. Suitable combination differences were found in both the ν₂ and the ν₄ infrared bands. The ground-state constants were assumed to be invariant to isotopic substitution at Ge, and the tensor distortion constants were held fixed at their microwave values. The results obtained are: B₀ = 2.69587 ± 0.00007 cm^?1, D₀ = (3.34 ± 0.03) × 10^?5 cm^?1, H₀ = (1.3 ± 0.5) × 10^?9 cm^?1.     

Intramolecular motion in the triptycenegermanyl radical: single crystal EPR study at variable temperature and DFT calculations

X-irradiation of single crystals of Tp–GeH₃ (Tp: triptycene) led to the trapping of the radical Tp–GeH₂. The angular variations of the resulting EPR spectra were recorded at 300 and 77 K. The drastic temperature dependence of the spectra was caused by both a strong anisotropy of the g-tensor and a rotation of the GeH₂ moiety around the C–Ge bond. The determination of the EPR tensors as well as the analysis of this motion required to take the presence of disorder in the crystal into account. In accordance with DFT calculations, Tp–GeH₂ is shown to be pyramidal and to adopt, in its lowest energy structure, a staggered conformation. Rotation around the C–GeH₂ bond is blocked at 90 K and is almost free above 110 K. The experimental barrier, obtained after simulation of the EPR spectra as a function of the rotational correlation time, is equal to 1.3 kcal mol⁻¹, which is slightly inferior to the barrier calculated by DFT (3.6 kcal mol⁻¹). Calculations performed on Tp–CH₃, Tp–GeH₃ and Tp–GeH₂ show that the rotation barrier ΔE_rot around the C–Ge bond drastically decreases by passing from the germane precursor to the germanyl radical and that ΔE_rot increases by passing from the germane to its carbon analogous. Structural parameters involved in these barrier differences are examined.     

Intensities and H2-broadened half-widths of Germane lines around 4.7 μm at temperatures relevant to Jupiter's atmosphere

Absolute intensities and H₂-broadened half-widths of R(0) and R(1) of ⁷²GeH₄ have been measured at 119.5, 150.3, 199.0, 250.0, and 296.0 K using a tunable diode laser and the sweep integration technique. The combined intensity of the v₃ bands of all of the five isotopic species of GeH₄ as well as that of the Q-branches alone have been measured independently at 294 K using the Wilson-Wells-Penner-Weber technique.     

Coriolis interaction in the local mode (n100;F2) combination states of GeH4

Coriolis interactions in local mode (n100) combination states of GeH₄ are studied. Three widely used local mode models, the normal mode model with Darling–Dennison resonance included (NMDD) model and the anharmonically coupled anharmonic oscillator (ACAO) model with two different kinds of bond stretching variable, were used to calculate the values of the interaction parameters. As a test of these three models, the Coriolis interaction parameters of the local mode (3100) combination bands of the ⁷⁴GeH₄,⁷²GeH₄ and ⁷⁰GeH⁴ species, recorded at a resolution of 0.015cm^-1 on a Bruker IFS120HR Fourier transform spectrometer, are compared with the calculated results. There is good agreement.     

Mechanism of GeH4 dissociation on Si(1 1 1)-(7 × 7)

Results of an STM study of dissociative GeH₄ adsorption on Si(1 1 1)-(7 × 7) at 300 K show that GeH₄ adsorbs under scission of two Ge-H bonds according to GeH₄(g) + 4db → GeH₂(ad) + 2H(ad). GeH₂ binds to two adatom dangling bonds in a bridged configuration, while the two released hydrogen atoms saturate two additional dangling bonds. The GeH₄ sticking coefficient under these conditions is 1.2 × 10⁻⁶, one order of magnitude smaller than for SiH₄.     

DFT study on dissociative adsorption of SiH4 and GeH4 on SiGe(1 0 0)-2 × 1 surface

SiH₄ and GeH₄ dissociative adsorptions on a buckled SiGe(1 0 0)-2 × 1 surface have been analyzed using density functional theory (DFT) at the B3LYP level. The Ge alloying in the Si(1 0 0)-2 × 1 surface affects the dimer buckling and its surface reactivity. Systematic Ge influences on the reaction energetics are found in SiH₄ and GeH₄ reactions with four dimers of Si^∗-Si, Ge^∗-Si, Ge^∗-Ge, and Si^∗-Ge (∗ denotes the protruded atom). On a half H-covered surface, the energy barriers for silane and germane adsorption are higher than those on the pristine surface. The energy barrier for silane adsorption is higher than the corresponding barrier for germane adsorption. Rate constants are also calculated using the transition-state theory. We conclude that the SiGe surface reactivity in adsorption reaction depends on the Ge presence in dimer form. If the surface Ge is present in form of Ge^∗-Ge, the surface reactivity decreases as the Ge^∗-Ge content increases. If the surface Ge prefers to be in form of Ge^∗-Si at low Ge contents, the surface reactivity increases first, then decreases at high Ge surface contents when Ge^∗-Ge prevails. The calculated rate constant ratio of GeH₄ adsorption on Si^∗-Si over Ge^∗-Ge at 650 °C is 2.1, which agrees with the experimental ratio of GeH₄ adsorption probability on Si(1 0 0) over Si(1 0 0) covered by one monolayer Ge. The experimental ratio is 1.7 measured through supersonic molecular beam techniques. This consistency between calculation and experimental results supports that one monolayer of Ge on Si(1 0 0) exists in form of Ge^∗-Ge dimer.     

A new method for determining relaxation energies by means of aes and xps and its application to silicon compounds

A new method is presented for the determination of the absolute dynamic relaxation energy R_D from experimental Auger parameters, the static dielectric constant and the plasmon energy of the solids. The relaxation energies of the Si 1s and 2p core levels in Si, SiC, SiO₂, Si₃N₄ and Na₂SiF₆ are investigated by comparing the experimental values with theoretical results from a semiempirical dielectric theory. Both the experimental and theoretical results are valid only for the least-bound Si 2p state. The calculated relaxation shifts ΔR_D^ea(1s) and ΔR_D^ea(2p) are in reasonable agreement with the experimental values, and describe the extraatomic polarization effect well also for a deep level.     

Absolute line strengths of 74GeH4 near 5 μm

Line positions and absolute line strengths were measured for 23 Q-branch lines of the ν₃ fundamental of ⁷⁴GeH₄ at 295 K, using an infrared tunable diode laser spectrometer. The spectral range covered was from 2109.9658 to 2110.6218 cm^?1. The average standard deviation of the measured line positions was 0.0006 cm^?1 and that of the line strengths was 3.4%. Vibrational transition dipoles were computed from the measured line strengths, which gave 1226 ± 172 cm^?2 amagat^?1 for the ν₃ integrated band intensity.     

The perturbations of line frequencies in high-J manifolds of the ν3 band of SF6

In the diode laser spectra of several P- and R-branches of high-J manifolds in the ν₃ band of SF₆ it has been observed that the lines are shifted away from the positions predicted by the diagonal F_A1pp^(4,R,R) approximation of Moret-Bailly. The shifts form a smooth function of the line positions across each manifold; this function can be represented empirically by a parabola, to which the measured wavenumbers fit within experimental accuracy. This phenomenon is explained here by model calculations for P-, Q-, and R-branch excited state levels that perturb each other through higher-order vibration-rotation interactions. In the analysis, eigenvalues calculated by second-order perturbation theory are compared with those obtained by diagonalization of the Hamiltonian.     

Analysis of the ν3 and ν1 infrared bands of GeH4

The high-resolution infrared spectrum of GeH₄ in the region 2020 to 2200 cm^?1 was analyzed. Most of the observed lines were assigned to transitions of the ν₃ and ν₁ bands of the five naturally occurring isotopic species. The spectrum was fitted by diagonalizing the v₃ = 1 and v₁ = 1 Hamiltonians coupled by the dominant vibration-rotation interaction term. For each isotopic species, about 100 transitions were fitted with an overall standard deviation of 0.006 cm^?1, using only 10 adjustable parameters. The five sets of parameters obtained are consistent with the expected isotope effects.     

Mass spectroscopy of sputtered neutrals and its application for surface analysis

Mass spectroscopic studies of the neutral particles sputtered by Ar⁺ions at energies around 1 keV from polycrystalline targets of 11 different metals have been performed, using a hf plasma maintained in pure argon at some 10^?4 Torr by electron cyclotron wave resonance as an ionizing medium as well as an effective ion source. Besides sputtered atoms Me₁ and molecules Me₂ with intensity ratios R₂₁ between Me₂ and Me₁ in the order of 10^?2 to 10^?1, neutral triatomic complexes Me₃ with corresponding ratios R₃₁ of some 10^?4 are found. Possible applications of the experimental method for surface analysis are discussed for previously air exposed polycrystalline Ta and Nb surfaces.     

Theoretical investigation of EPR and optical spectra of Mo(V) in [Mo6O19][N(C4H9)4]3 salt

The electron paramagnetic resonance (EPR) spectral data (the g factors and hyperfine structure constants) and d–d transition spectra for the tetragonal Mo⁵⁺ centre in [Mo₆O₁₉][N(C₄H₉)₄]₃ salt are theoretically investigated from the complete diagonalization method (CDM) for a 4d¹ ion in tetragonally compressed octahedron. The theoretical results are in good agreement with the experimental data. The dependency of the g factors of the ground state on the R_∥(MoO bond length) has been studied. It is shown that the g factors varied with the R_∥ approximately in a linear way.     

A Comparison of Three Commercial Perfluorocarbon Emulsions as High-Field 19F NMR Probes of Oxygen Tension and Temperature

The increasing use of perfluorocarbons (PFCs) as probes of tissue oxygenation on the basis of the ¹⁹F spin-lattice relaxation rate (R₁) prompts comparison between several commercially available PFC blood-substitute emulsions, The relative sensitivities to both oxygen and temperature of the emulsions Oxypherol, Oxygent, and Fluosol at 7 T have been investigated, The linear response of R₁ with pO₂ was confirmed for each resonance in the range 4-50°C, In general, R₁ is not a linear function of temperature, and we demonstrate this for perfluorotributylamine (FTBA) over an extended range of temperatures, 239-343 K. Theoretical R₁ values of FTBA were compared with experimental data by computer modeling of relaxation mechanisms, To further understand the structure-function relationships of PFCs, 2D COSY experiments were used for the assignment of resonances and as an aid in interpretation of relaxation mechanisms, Finally, the utility of Oxygent and Oxypherol for measuring tissue pO₂ in perfused rat hearts was compared before, during, and after eight minutes of global ischemia.     

Formation of Ge nanocrystals and evolution of the oxide matrix in as-deposited and annealed LPCVD SiGeO films

SiGeO films were deposited by LPCVD using Si₂H₆, GeH₄ and O₂ as reactive gases and furnace annealed to segregate the possible excess of Si and Ge in the form of nanocrystals embedded in an oxide matrix. For low GeH₄:Si₂H₆ flow ratios and deposition temperatures of 450 ^°C or lower, the deposited film consists of a SiO₂ matrix incorporating Ge. No Ge oxides and no nanocrystals are detected. After annealing of the samples with SiO₂ matrices at temperatures of 600 ^°C or higher, quasi-spherical isolated Ge nanocrystals with diameters ranging from 4.5 to 9 nm and homogeneously distributed throughout the whole film thickness are formed. In the samples deposited with low GeH₄:Si₂H₆ flow ratios, the original SiO₂ matrix holds its composition.     

Interactions of germanium atoms with silica surfaces

GeH₄ is thermally cracked over a hot filament depositing 0.7-15 ML Ge onto 2-7 nm SiO₂/Si(1 0 0) at substrate temperatures of 300-970 K. Ge bonding changes are analyzed during annealing with X-ray photoelectron spectroscopy. Ge, GeH_x, GeO, and GeO₂ desorption is monitored through temperature programmed desorption in the temperature range 300-1000 K. Low temperature desorption features are attributed to GeO and GeH₄. No GeO₂ desorption is observed, but GeO₂ decomposition to Ge through high temperature pathways is seen above 750 K. Germanium oxidization results from Ge etching of the oxide substrate. With these results, explanations for the failure of conventional chemical vapor deposition to produce Ge nanocrystals on SiO₂ surfaces are proposed.     

An investigation of range distribution parameters of implanted 19F ions in Au,Ag and Cu noble metals

Depth profiles of fluorine implanted in gold, silver and copper metal have been accurately measured using the ¹⁹F(p,αγ)¹⁶O resonance nuclear reaction at E_R = 872.1 keV. A proper deconvolution calculation method was used to extract the depth profile of fluorine from the experimental excitation yield curves. The range parameters, R_p, ΔR_p, and SK obtained in this work were compared with the theoretical calculations. The comparison shows that for all materials studied here the experimental R_p values are in good agreement with the results obtained by the TRIM96 code, while the experimental range stragglings, ΔR_p, are systematically larger than the TRIM simulation results.     

Absorption of carbon tetrafluoride at 16 μm. Analysis of the ν4 band

The absorption spectrum of ¹²CF₄ was recorded between 595 and 670 cm^?1 with a resolution of 0.010 cm^?1. About 900 line clusters belonging to the ν₄ band were assigned, ranging from P(70) to R(70). A linear least-squares fit on 867 of these data led to six significant spectroscopic constants, allowing to reproduce the experimental wavenumbers with an overall standard deviation of 0.003 cm^?1.     

Two-dimensional sequence of shapes for cold-fission of264Fm

The neutron-rich²⁶⁴Fm should be the best cold-fissioning nucleus, owing to the strong shell effect of the doubly magic fragments¹³²Sn. The optimum cold fission path in the plane of two independent shape coordinates, the separation distanceR and of the radius of the light fragmentR ₂, is determined. Werner-Wheeler inertia tensor and Yukawa-plus-exponential deformation energy are used to calculate the action integral. Microscopic shell and pairing corrections are based on the asymmetric two-center single-particle model. Different variation lawsR ₂=R ₂(R), for the fission trajectory were tested: polynomials of 2nd, 3rd, and 4th degree and an exponential function. The partial half-life for cold fission is estimated to be several orders of magnitude shorter than that of α-decay.     

A possible interpretation of enhanced raman scattering in the vicinity of a nanotip

Theoretical and experimental studies on Raman scattering in a space with small bodies are briefly reviewed. Probabilities of radiative transitions for atoms (molecules) in the vicinity of bodies with dimensions much smaller than a wavelength are calculated. It is shown that in the vicinity of a nanosphere with |ε|?1, the probability of a single-photon electric dipole transition increases by a factor of 9, and the probability of a two-photon transition—by a factor of 81. In the vicinity of a conical needle resting on a plane (the needle and plane have |ε|?1), the radiative transition probability increases by a factor (λ/R _in)² and (λ/R _in)⁴ for single-and two-photon transitions, respectively (R _in is the radius of the needle tip curvature). This theoretical result is offered to interpret the enhancement of radiative processes experimentally observed in the referenced studies.