Calculations of impact broadening and shift of spectral lines for realistic interatomic potentials

We have studied theoretically the impact broadening and shift of the resonance doublets of Rb and Cs for the interatomic potential data of Baylis and Pascale, which were determined from ab initio calculations. We show that, without introducing any adjustable parameter, we obtain good agreement between theoretical and experimental values for both the P_1/2 and the P_3/2 component. In the latter case, the theoretical results are significantly modified when anisotropy of the interaction potential is taken into account.     

Widths and shifts of HF vibration-rotation absorption lines induced by pressure of rare gases

Widths and shifts of the HF vibration-rotation absorption spectrum, induced by the pressure of rare gases, have been calculated using the Kolb-Griem-Baranger theory, for the pure rotation, 0–1, and 0–2 bands. Agreement between the calculated and experimental widths is good in general, but the calculated shifts, though having a qualitatively correct m-dependence for the most part, exceed the experimental values by a factor of 1·3-2·0. Isotropic effects are included to all orders, leading to three major consequences: (1) a criticism is made regarding one of the assumption underlying Anderson's approximation number two, (2) a reason is provided for the differences in widths of R and P branch lines of the same ∣m∣ within a given band, and (3) the previously unexplained increase in widths with increasing ∣m∣ in the 0–2 band with xenon is explained.     

Pressure broadening and shifting parameters for the spectral lines in the fundamental vibration-rotation bands of HBr and HI in mixtures with rare gases

We report measurements of the line broadening and shifting coefficients in the (1 ← 0) fundamental absorption bands of the HBr and HI molecules in mixtures with rare gases He, Ne, Ar, Kr, and Xe. Comparison is given with the published data on other HHal-Rg systems. The measured line shifts are separated into terms symmetric and asymmetric in the line number m. The magnitudes of the symmetric shifts change in a regular manner in the series of rare gases and reach perturber-specific asymptotic values at higher ∣m∣. It is found that the asymptotic values of the symmetric line shifts linearly correlate with the respective C₆ potential energy constants and that the slopes of these correlations are proportional to the vibrational ground state dipole moments squared of the hydrogen halide molecules.     

Nonwetting and sticking of the heavy rare gases on potassium surfaces

We have investigated the adsorption, growth, and desorption of Ar, Kr, and Xe on K mono- and multilayers on Ru(001) at 6.5 K. In all cases, three-dimensional growth from very low rare gas (RG) coverages on, clearly indicates nonwetting, and the desorption energies for low RG coverages are much lower than the RG sublimation energies, and lower on K multi- than on K monolayers. Nevertheless, initial sticking coefficients of the RG on both types of K layers are well defined and not dominated by nucleation or by impurities or defects. Their values and dependence on type of substrate can be understood qualitatively, and quantitatively for Ar in terms of a recently developed quantum mechanical model, extending adsorption dynamics studies to nonwetting systems.     

Pressure broadening and shifting parameters for the spectral lines in the first overtone vibration-rotation bands of HBr and HI in mixtures with rare gases

We present experimental data on the previously unknown line broadening and shifting coefficients in the (2 ← 0) overtone vibration-rotation bands of the HBr and HI molecules in mixtures with several rare gases. The vibrational dependence of the isotropic and anisotropic components of the binary interaction potential is probed by separating the measured line shifts into parts symmetric and asymmetric in the line number m and by comparing with the previously published similar data for the fundamental bands of the same molecules. It is shown that the line shifts are dominated by the vibrational dependence of the isotropic potential. A linear correlation is found between the asymptotic values of the symmetric shifts in the overtone bands for all HX-Rg (X = F, Cl, Br, I) pairs and the respective C₆ long-range potential energy constants. Line broadening parameters in the overtone band of pure HBr are also reported.     

Interpretation of measured spectral line shapes using a square-well potential: The absorption lines of cesium broadened by rare gases

A simple square-well potential is used as an aid in understanding the complicated evolution of the absorption lines and their associated satellites for cesium perturbed by the rare gases. New experimental halfwidth data for cesium perturved by Xe, Ar, and He are presented. In the case of Xe, data for the second, third and fourth members are presented to 30, 7, 1 rd (relative density), respectively. For Ar, data are presented for the third through the ninth member. The pressure range for the third and fourth members is from 0 to 20 rd. For the other members, it ranges to 8 rd for the fifth and to 2 rd for the ninth. Third and fourth member helium data are presented to about 20 and 8 rd, respectively. Several theoretical computer profiles are used to illustrate the evolution of the line and satellites with foreign gas pressure and these are compared with the experimental data.     

High pressure calculation of the melting curve: Na,K, Rb and Cs

The melting of four alkali metals is investigated in the present paper, in the theoretical framework defined in a preliminary study on sodium. The calculations enable us to predict the existence of a very flat maximum on all four phase lines. The obtained results are in good agreement with experiment in the case of Na, K and Rb, and emphasize the importance of “d” effects and the dramatic influence of the electronic transition on the high pressure fusion curve of Cs.     

The far-wing broadening of the Na D lines by K,Rb and Cs and the electrostatic interaction potentials of the NaK,NaRb and NaCs molecules

The far wings of the NaD lines broadened by K, Rb and Cs have been measured in absorption by scanning a single-mode dye laser across the lines and detecting the flourescence signal. The relative absorption coefficients for the NaRb and NaCs are normalized using the impact widths recently measured by Kamke et al. The found red asymmetries of the lines are surprising results when only the theoretical van der Waals interactions are taken into account. It is demonstrated that the addition of dipole-quadrupole forces is necessary to explain the experimental findings. Using the extended electrostatic interaction potentials the theoretical impact widths of the NaD lines by Rb were found to be in agreement with the experimental data of Kamke et al.     

Departure from the law of rectilinear diameters for fluids Rb and Cs with delocalized electrons

Terekhov has recently presented a phenomenological model to describe the liquid-vapour critical point. While Terekhov's model embraces a number of equations of state, including both Van der Waals and Dieterici, it leads to the Law of Rectilinear Diameters (LRD). This restricts the applicability to insulating fluids such as Ne and Ar. For the heavy alkalis, Rb and Cs, with delocalized electrons, there are substantial departures from the LRD, which may be due to long-range polarization interaction between the metallic ions.     

Asymptotic completeness for quantum-mechanical potential scattering: II. Singular and long-range potentials

The geometrical proof for the asymptotic completeness of the wave operators and the absence of a singular continuous spectrum of the Hamiltonian is extended to cover singular potentials where the Hamiltonian is defined as a form sum, and long-range interactions like Coulomb forces.     

Measurement of the total cross sections of ultracold neutrons with noble gases and search for long-range forces

The comparison of results of cross section measurements by the different methods can provide useful information on existence of long-range interaction. The total neutron cross sections of He, Ne, Ar, Kr, and Xe were measured using a method of ultracold neutrons. Measurements with ultra cold neutrons confirm the discrepancy between coherent cross-section of scattering for He measured by a neutron interferometer and scattering cross-section measured by the transmission method. The discrepancy makes up 5.3 standard deviations.     

Calculated electrode-edge effects in flash-excited charge-transits and comparison with measurements on Sulphur

Current-time (transit, profiles for charge flash-excited near edges of “sandwich” electrodes have been obtained theoretically and experimentally (the latter for electrons in sulphur). Agreement is good for all three electrode configurations considered, namely small-large, large-small, small-small. Characteristic features are high-current spikes at short time, rising currents during the transit and current tails extending to twice the normal transit time. The effects are relevant when “overall” flash excitation is used, and non-appreciation of them could lead to substantial misinterpretation of results on a variety of materials. Present results for sulphur give an electron mobility of about 4.5 × 10^?8 m² V^?1 s^?1.     

Search for superdense nuclei of Rb and Cs among the products of 8 GeV proton interactions with Ta

Experimental searches for β-active superdense nuclei of Rb and Cs among the products of 8 GeV proton interactions with Ta are described. The method of selective off-line mass-separation with scanning of the β-activity distribution on the collector was used. According to π-condensation theory, the long-lived anomalous nuclei are expected to be more neutron-deficient than the usual ones. Moreover, their mass numbers may be significantly nonintegral measured on the normal mass scale, because of unusual binding energy. These predictions guided the present search. No anomalous nuclei were found. The upper limit for Rb nuclei in the range 69 ? A ? 78 is 10^?5 with respect to the yield for ⁸¹Rb; for Cs in the range 112 ? A ? 122 the limit is (5–10) × 10^?6 of the yield for ¹²⁷Cs. These estimations are based on the assumption that the half-life of superdense nuclei equals 5 h.     

Vibrational properties of Cs4W11O35 and Rb4W11O35 systems: high pressure and polarized Raman spectra

Cs₄ W₁₁O₃₅ (CW) and Rb₄ W₁₁O₃₅ (RW) belong to the class of hexagonal bronzes whose structure originates from the K_xWO₃ superconductor hexatungstate. Charge‐imbalanced tungsten bronzes are dielectric materials with rich polymorphism, ferroelectric properties and second‐harmonic generation. In this work, we report the polarized Raman spectra results for both CW and RW, as well as results of high‐pressure Raman scattering experiments (0.0–11.0 GPa) for the Cs₄ W₁₁O₃₅ system, in which we have observed two structural phase transitions at ∼4 and 7.5 GPa. We discuss these transformations and polarized Raman spectra on the basis of lattice dynamics calculation in the related system KNbW₂O₉. Polarized Raman spectra provide strong indication that the highest wavenumber modes observed in these systems originate from tungsten or oxygen vacancies. The observation of a soft‐like mode indicates that the observed phase transitions exhibit a displacive‐type behavior, thus further indicating that these transformations are likely related to reorientations of the octahedral units. The soft mode nature is discussed as well. PACS: 77.80.Bh; 78.30.Hv; 78.30.‐j. Copyright © 2010 John Wiley & Sons, Ltd.     

Empirical construction of interatomic potentials for studies of grain boundaries and other crystal defects: Pure metals and binary alloys

It is first argued that pair potentials are physically meaningful if they are regarded as describing interaction between atoms embedded in an environment of similar density as that for which their derivation was made. These potentials are capable of describing structural aspects of lattice defects but not the cohesive properties. Guidelines for determination of the shape of potentials and an empirical scheme for their construction in pure metals is then outlined. It is shown that this method when applied to simple metals leads to potentials similar to those obtained on the basis of a pseudopotential theory and extension of this scheme to other metals is discussed. An empirical scheme of construction of potentials for binary alloys is then briefly described. It is shown that concentration dependences of elastic constants and lattice stability evaluated using these potentials agree with experimental data and thus these potentials are suitable for studies of defects in binary alloys.     

Tunable-laser derivative spectroscopy on spectral lines with combined Doppler and collision broadening

In derivative spectroscopy, we optimize the measurement sensitivity by utilizing the maximum excursion of the derivative of the spectral absorption coefficient as a single spectral line is scanned. Results for lines with pure Doppler or Lorentz contour have been given previously. We present here the required spectroscopic data for spectral lines with combined Doppler and collision broadening.     

Sputtering gases and pressure effects on the microstructure,magnetic properties and recording performance of TbFeCo films

The MsHc value is considered to be a key factor in high-density recording, and controlling the microstructure on the magnetic underlayer was found to be an effective way of increasing the MsHc of the amorphous TbFeCo magneto-optical (MO) medium. In this paper, we investigate the TbFeCo film's magnetic properties and the effects on the microcolumnar structure, which depends on the sputtering conditions of using various sputtering gases including Ar, Kr, and Xe, and the recording characteristics of TbFeCo memory layers. With heavy sputtering gases such as Kr or Xe, the columnar structure can be prepared in a TbFeCo film at a pressure lower than 1.0 Pa. The columnar structure of a recording layer can be effectively formed thanks to the effects of the magnetic underlayer, which has a fine surface even in the sputtering process in which Xe gas is used. The above applies to the sputtering process in which Ar gas is used. Also, when Xe gas is used in the sputtering process, coercivity Hc is increased through the formation of a well-segregated microcolumnar structure built on domain wall pinning sites, and we obtain a large MsHc and a high squareness ratio of the Kerr-hysteresis loop. Our results indicate that processing a TbFeCo film with heavy sputtering gases is suitable for tiny mark stability because the temperature gradient of Hc is increased. The objective of the low-pressure sputtering process using Xe gas to produce the columnar structure is to achieve ultra-high-density recording with tiny mark stability in the TbFeCo medium. This has been confirmed with magnetic force microscope (MFM) images of stable tiny marks recorded on TbFeCo film.