Quantum properties of strong accumulation layers on ZnO surfaces

Extremely strong accumulation layers with surface electron densities ΔN approaching 10¹⁴ cm^?1 have been achieved on ZnO surfaces in contact with an electrolyte. Quantization effects, which are very pronounced in such narrow (?10 Å) layers, are studied by measurements of ΔN versus surface barrier height V_s. Comparison of the results with self-consistent calculations shows very good agreement up to ΔN = 2 × 10¹³ cm^?2. Deviations observed at higher ΔN are probably associated with the huge electric fields (～10⁷ V/cm) experienced by the surface electrons.     

Ab initio determination of the torsional spectra of acetic acid

The torsional potential energy surface and the favourite geometries of acetic acid are determined with MP4/cc-p VTZ ab initio calculations. The molecule shows two planar trans and cis conformers whose energy difference is 1882.7 cm^?1. Both minimum energy geometries are separated by a barrier of 4432.1 cm^?1. The most stable trans-conformer shows a quite low methyl torsion barrier of 169.8 cm^?1. The roto-torsional energy levels have been calculated up to J = 10. The two torsional fundamental frequencies of the trans-conformer, the methyl and the OH torsion are 82.857 (A²) and 77.050cm^?1 (E) and 568.532 (A²) and 568.418cm^?1 (E). The V₃ barrier causes a splitting of 0.315cm^?1 in the ground vibrational state where the quartic centrifugal distortion constants have been predicted to be D_J = 90.4kHz, D_JK = ?301.5kHz and D_K = 165.4kHz. Finally, the far-infrared spectra of two isotopomers have been simulated from ab initio calculations.     

Far infrared absorption of amorphous GaAs and Ge

Far infrared reflection spectra of amorphous GaAs and Ge have been obtained in the frequency region from 30–600 cm^?1. For each material, curves of ω?₂ vs frequency have been obtained whose corresponding reflectivity curves give a best fit to the data. The peak value of the abdorption coefficient is about 4000 cm^?1 for GaAs and 160 cm^?1 for Ge. The results are compared with Raman spectra and with theoretical calculations.     

Molecular Dynamics simulations of borate glasses

Abstract

The results of Molecular Dynamics simulations of borate glass (B₂O₃) using three-particle interactions are presented. These calculations yield a glass consisting of randomly connected BO₃ triangles. Infrared and Raman spectra have been calculated and compared with experimental spectra. The calculated infrared spectra show two main bands, one at 650 cm^?1 and one at 1250 cm^?1, in agreement with experiment. The Raman spectra reproduce the experimental peak at 805 cm^?1 but the peak width is a factor of ten too large. Apparently, the simulated glasses have less short range order than the laboratory glasses.     

A refined estimate of the bond length of methane

The atmospheric reaction of H₂S with Cl was investigated using high level ab initio calculations and Canonical Variational Transition State Theory (CVTST). The adduct formation step is the dynamical bottleneck, and the rate constant was calculated to be 1.2 × 10^?9 cm³ molecule^?1 s^?1, which is around ten times greater than the upper experimental value. Additional ab initio classical trajectory calculations show that the adduct formed in the initial collision can easily dissociate, recrossing the variational transition state. The stabilization of this species depends on the vibrational excitation of H₂S molecule, which requires an almost collinear SH-Cl collision. These dynamical effects provide an explanation for the substantial error in the rate constant obtained using CVTST.     

Comparison of band model and integrated line-by-line synthetic spectra for methane in the 2.3 μm region

The 2.3 μm spectral region of methane can be used to retrieve cloud properties of planetary spectra, provided parameters for the methane spectrum are known. Two standard techniques for calculating absorption spectra in this region are compared here. A Voigt profile Mayer-Goody random band model is applied, using coefficients empirically fitted by Fink et al. to CH₄ spectra recorded with high absorping amounts at 10 cm^?1 resolution. Calculation of the absorption is also done with a line-by-line direct integration method for the same gas conditions using molecular parameters obtained by combining an older unpublished list of observed positions and estimated line strengths (derived from 0.04 cm^?1 resolution data) with quantum assignments from the literature. The molecular parameters have been evaluated for the 4180–4590 cm^?1 region by comparing new laboratory spectra with 0.01 cm^?1 resolution recorded at 296 and 153K with synthetic spectra calculated at the same conditions. The deficiencies of the molecular parameters and random band coefficients for this spectral region of CH₄ are then discussed qualitatively and demonstrated by comparing 10 cm^?1 resolution synthetic spectra calculated by both methods for the same gas conditions at 296, 153, and 55 K.Curves of growth of the total equivalent width are calculated at 296 and 55K for a pathlength of 50 cm and pressures up to 10 atm. Changing the mean line spacing in the band model gives better agreement between the spectra calculated by the two techniques at low gas temperatures. The required multiplier has been determined for the mean line spacing for pressures from 10^?6 to 10^?1 atm at 55, 100, and 150 K.     

Far-infrared absorption of MgO: Fe2+ in magnetic fields

We have measured the far-infrared absorption of iron-doped MgO in the wavenumber region 10–200 cm^?1 and in magnetic fields up to 6 T. Absorption peaks found at 107.0 and 110.5 cm^?1 are assigned to magnetic dipole transitions between the spin-orbit Г_5g groundstate (J = 1) and the Г_3g, Г_4g excited states (J = 2) of the Fe²⁺ -ion at a cubic site. The observed magnetic field dependence shows that Г_4g is the higher excited level, so that the crystal field order of the levels is not changed by the reduction of the spin-orbit splitting attributed to a dynamic Jahn-Teller effect. An additional absorption peak at 33.4 cm^?1 is found to split in magnetic field.In iron-doped KMgF₃ absorption peaks at 52 and 87 cm^?1 that have previously been attributed to the same transitions of Fe²⁺ are found to remain unshifted and unsplit in magnetic fields up to 6 T.     

Einstein A-coefficients for rotational transitions in the HN2O+

EinsteinA-values for the electric dipole transitions between the rotational levels up to 540 cm⁻¹ andJ=11 in the ground vibrational state of the protonated N₂O (i.e., HN₂O⁺) are calculated. The coefficients are used to compute the mean radiative lifetimes of the levels. TheseA-values can be used for analysing the spectra from astronomical objects, if observed.     

The rotational spectrum of water between 650 and 50 cm−1: H218O and H217O in natural abundance

In the far infrared spectrum of water, 121 H₂¹⁸O and 48 H₂¹⁷O pure rotational lines have been identified. From the line frequencies and a minimum number of literature values of near infrared rotation-vibration transitions and lines from microwave spectra, the ground-state energy levels have been calculated up to J = 12 and 11, respectively. For low J levels, the agreement with earlier calculations from other microwave lines and near infrared results is within the experimental error, but deviations up to 0.6 cm^?1 are found for high J, high K_a levels.     

Absolute integrated intensity and individual line parameters for the 6·2μ band of NO2

The absolute integrated intensity of the 6·2μ band of NO₂ at 40°C was determined from quantitative spectra at ~ 10 cm^?1 resolution by the spectral band model technique. A value of 1430±300 cm^?2 atm^?1 was obtained. Individual line parameters, positions, intensities and ground state energies were derived, and line-by-line calculations were compared with the band model results and with the quantitative spectra obtained at ~ 0·5 cm^?1 resolution.     

Spin-dependent phonon Raman scattering in CdCr2Se4

Influences of ferromagnetic ordering on the phonon Raman scattering are studied for CdCr₂Se₄ through the intensity measurements of Raman spectra between 25 and 300 K with various wavelengths of excitation light (488.0–676.4 nm). Spin-dependent enhancements of Raman cross section are observed for optical phonon lines D(168 cm^?1) and F(238 cm^?1) with excitation wavelengths of about 630 and 550 nm, respectively. This kind of phenomenon in spinel-type chalcogen chromites seems to originate in spin-dependent intermediate interactions in the excited states of specific electronic transitions with which the incident or scattered light is resonant.     

Absorption spectrum of trideuteromethane between 7 and 11 μm. Analysis of the ν5 band

The absorption spectrum of trideuteromethane was recorded in the range 900–1400 cm^?1 with a resolution of 0.020–0.025 cm^?1. The ν₅ band centered at 1292.499 cm^?1 is analyzed here. A fit based on 869 observed transitions including J′ values up to 22, leads to a set of spectroscopic constants suitable for energy calculations in the upper-state v₅ = 1. These constants reproduce the experimental wavenumbers with a standard deviation equal to 0.008 cm^?1. The tabulated line strengths are calculated on the basis of the value S = 27.1 cm^?2 atm^?1 at 300 K, measured by Hiller and Straley, for the band strength of ν₅. A useful comparison is made between the values now derived for some constants and the corresponding ones predicted by Gray and Robiette in their recent force field calculations of methane and isotopic species.     

Coherent Stokes and anti-Stokes Raman spectra of the ν1 (A1) and ν2 (E) bands of SF6 and UF6

Coherent Stokes and anti-Stokes Raman scattering are used to study the ν₁ and ν₂ spectral band profiles of UF₆ and SF₆. Most of the observed SF₆ “hot” bands are assigned, leading to evaluations of the anharmonicity constants X_ij: X₁₂ = ?(2.80 ± 0.30) cm^?1, X₁₄ = ?(1.00 ± 0.15) cm^?1, X₁₅ = ?(1.00 ± 0.15) cm^?1. For UF₆, a tentative assignment of the “hot” bands is made: X₁₂ = ?(1.80 ± 0.30) cm^?1, X₁₃ = ?(1.60 ± 0.30) cm^?1, X₁₄ = ?(0.20 ± 0.10) cm^?1, X₁₅ = ?(0.25 ± 0.10) cm^?1, and X₁₆ = ?(0.10 ± 0.05) cm^?1. Parameters such as the vibration-rotation coupling constants are determined. For SF₆: α = (7 ± 2) × 10^?5 cm^?1 for the ν₂ band and α = ?(1.02 ± 0.01) 10^?4 cm^?1 for the ν₁ band. The calculated spectral profiles of the coherent Stokes or anti-Stokes spectra, which are in good agreement with experimental results, give values for the resonant and nonresonant parts of the susceptibility in both molecules. They also show, in some cases, the influence of neighboring combination bands.     

Brillouin scattering observation of phonon renormalization in KC1:CN−

The phonon-defect interaction in KC1:CN^? has been studied in the 16 GHz frequency range using the Brillouin scattering technique. Brillouin spectra of KC1:CN^? at 4.2 K show a defect induced phonon velocity renormalization. The measurements are consistent with a 〈111〉 oriented CN^? dipole in KC1 with a tunneling level of T_2g symmetry at 2.6 cm^?1 and a coupling constant of 1.5 × 10^?21 cm³.     

Synthetic atmospheric transmittance spectra near 15 and 4.3μm

Synthetic monochromatic atmospheric transmittance spectra are presented for infrared intervals in the vicinity of the 15 and 4.3μm CO₂ bands. The intervals are nominally 20 cm^-1 in width, and the spectra partition the intervals [560, 780] cm^-1 and [2180, 2400] cm^-1, respectively. The spectra are for a vertical atmospheric path. A given spectrum is presented at that pressure for which the mean weighting function $\text{(-d}\text{Tau (P)}\text{?d ln P)}$ is a maximum. In order to indicate the molecular origin of the features in a given spectrum, separate spectra are also presented for those species which make center line contributions to the absorption over the interval. The transmittance model for the calculations is described. In addition to the representation of spectral features for intervals which comprise these two CO₂ bands, the spectra afford a utility in the design of high precision satellite temperature radiometers.     

Extended assignment and analysis of the ν2 and ν4 infrared bands of 12CH4

Infrared spectra of the ν₂ and ν₄ bands of ¹²CH₄ have been assigned up to J′ = 20 in the ν₄ band and J′ = 17 in the ν₂ band. Assignments are presented for over 1000 transitions ranging from 1123 to 1712 cm^?1, which involve 652 upper-state energy levels of the two bands. The 652 upper-state levels have been fitted with a weighted standard deviation of 0.0026 cm^?1, almost all levels being reproduced to within their experimental error, by a Hamiltonian for the coupled upper states containing 28 refining parameters and 4 fixed parameters. Calculated relative intensities are also tabulated and discussed in relation to recent experimental intensity measurements.     

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.     

High resolution infrared synchrotron study of CH2D81Br: ground state constants and analysis of the ν5, ν6 and ν9 fundamentals

The high resolution infrared absorption spectrum of CH₂D⁸¹Br has been recorded by Fourier transform spectroscopy in the range 550–1075?cm^?1, with an unapodized resolution of 0.0025?cm^?1, employing a synchrotron radiation source. This spectral region is characterized by the ν₆ (593.872?cm^?1), ν₅ (768.710?cm^?1) and ν₉ (930.295?cm^?1) fundamental bands. The ground state constants up to sextic centrifugal distortion terms have been obtained for the first time by ground-state combination differences from the three bands and subsequently employed for the evaluation of the excited state parameters. Watson's A-reduced Hamiltonian in the I^r representation has been used in the calculations. The ν ₆?=?1 level is essentially free from perturbation whereas the ν ₅?=?1 and ν ₉?=?1 states are mutually interacting through a-type Coriolis coupling. Accurate spectroscopic parameters of the three excited vibrational states and a high-order coupling constant which takes into account the interaction between ν₅ and ν₉ have been determined.     

Low temperature subband 2D electron mobilities in heavy delta- and modulation doped GaAs/GaAlAs heterostructures

We synthesised high-2D electron-density GaGs/GaAlAs heterostructures with different distance L_σ of Si delta-layer in GaAs from the heterojunction and uniform doped GaAlAs. The quantum Hall effect and Shubnikov-de Haas effect were measured for temperatures down to 0.4 K in magnetic fields up to 40 T. The enhanced 2D electron concentration achieved was 1.1^*10¹³ cm^?2 in six filled subbands. The Hall mobility depends on L_σ and has maximum for L_σ=600÷750Å. From the amplitudes of the SdH oscillations and Fourier transforms the subband mobilities and electron concentration in each subband have been extracted. According to calculations intersubband electron scattering appears to be important and reduces mobilities in subbands.     

High-frequency and -field electron paramagnetic resonance of high-spin manganese(III) in axially symmetric coordination complexes

High-frequency and -field electron paramagnetic resonance (HFEPR) has been used to study several complexes of high-spin manganese(III) (3d⁴,S = 2): [Mn(Me₂dbm)X] and [Mn(OEP)X] (X = Cl^?, Br^?), where Me₂dbm^? is the anion of 4,4′-dimethyldibenzoylmethane and OEP^2? is the dianion of 2,3,7,8,12,13,17,18-octaethylporphine. These non-Kramers (integer spin) systems are not EPR-active with conventional magnetic fields and microwave frequencies. However, use of fields up to 15 T in combination with multiple frequencies in the range of 95–550 GHz allows observation of richly detailed EPR spectra. Analysis of the field- and frequency-dependent HFEPR data allows accurate determination of the following spin Hamiltonian parameters for these complexes: [Mn(Me₂dbm)Cl],D = ?2.45(3) cm^?1; [Mn(Me₂dbm)Br],D = ?1.40(2) cm^?1; [Mn(OEP)Cl],D = ?2.40(1) cm^?1; [Mn(OEP)Br],D = ?1.07(1) cm^?1 (E ≈ 0, andg ≈ 2.0 in all cases). Comparison of structural data with the electronic parameters for these and related complexes shows quantitatively the effects of axial and equatorial ligation on the electronic structure of Mn(III). These high-spin complexes can be employed as building blocks in the construction of single-molecule magnets. Thus the accurate determination and understanding of the electronic properties, best obtainable by HFEPR, of these monomeric units is important in understanding and improving the properties of the polynuclear single-molecule magnets which can be formed from them.