Experimental relative line strengths within selected multiplets of neutral sulfur from the visible and infrared spectral range

In a wall-stabilized cascade arc helium plasma with some traces of SF₆ has been generated. On the basis of measured total line intensities emitted from the plasma, the relative line strengths within twelve multiplets of neutral sulfur (SI) have been determined. The studied lines cover the spectral range from 415 nm to 1046 nm. The obtained experimental line strengths are compared with results of recent theoretical data as well as with results of older experiments. In addition the SI line strength data are compared with analogous transitions in the OI spectrum.     

The influence of non-radiative transitions on bombardment induced photon emission from Ti and Ti oxide

Photon yields from Ti atoms sputtered from Ti and Ti oxide due to 55 keV Ar⁺ and O₂⁺ ion bombardment have been studied. Photon yields and line profiles of selected lines have also been studied as a function of background O₂ exposure. An attempt has been made to correlate changes in yields and line shapes with variations of the band structure in the solid. Resonance ionization processes are shown not to contribute to the observed yield, however Auger processes cannot be excluded. Lifetime effects have a strong influence on the observed results. It is shown that the distribution of excited states produced by the ion bombardment is Boltzmannlike. We note that it is possible to interpret these results in terms of a model which assumes that the probability of excitation or ionization is exponentially dependent on the excitation or ionization energy, without invoking electron exchange mechanisms.     

The absorption line profiles of H2O near 1.39 μm in binary mixtures with N2, O2, and H2 at low pressures

The absorption line profiles of water vapor in binary mixtures with diatomic molecules H₂, N₂, and O₂ have been recorded on a diode laser spectrometer. The profiles of several lines of the 101 band have been studied near 1.39 μm with a spectral resolution of 3 × 10^?4 cm^?1. The pressure of the binary mixtures was varied from 0 to 200 Torr. The experimental data obtained have been used to test the Voigt, Rautian-Sobel’man, and Galatry theoretical models of a spectral line profile. The coefficients of collisional narrowing have been determined from the results of the fitting.     

Shifting and line mixing parameters in the ν4 band of NH3 perturbed by CO2 and He: Experimental results and theoretical calculations

The pressure-induced shifting coefficients and line mixing parameters have been studied in the ν₄ band of NH₃ perturbed by CO₂ and He at room temperature. Measurements have been made using a high-resolution Fourier transform spectrometer. The measurements cover the ^PP and ^RP branches of the ν₄ band and are located in the spectral range 1470-1600 cm⁻¹. The line shift and line mixing parameters have been derived from a non-linear least-squares multi-pressure fitting technique. The shift coefficients are compared to a semiclassical calculation based on the Robert-Bonamy formalism employing two types of intermolecular interactions. It is shown that the line shifts mainly originate from the vibrational dephasing effects. The observed interference parameters are compared with calculations based on state-to-state collisional cross sections calculated from the intermolecular potential with a semiclassical approach. The results of computation are in reasonable agreement with the experimental data. It is demonstrated also that the line mixing process mainly originates from the energy transfer between symmetric and antisymmetric components of the inversion doublets.     

Influence of line interference on the vibration-rotation band shapes

The shapes of the CO, v₃, CO₂, and v₃ N₂O fundamental vibration-rotation bands have been studied at various temperatures and in the presence of several perturbing gases. Also the half-widths of CO vibration-rotation lines have been measured at 78 K. In the region of line wings, the measured absorption coefficients deviate from those given by the superposition of Lorentzian profiles. These deviations are explained by the collision-induced line interference that causes redistribution of absorption inside the band. A theory of line mixing is formulated which is based on Markov approximation and on the strong collision model. Simple analytical expressions are obtained for the band shape. The computed shapes are in satisfactory agreement with the experimental results. The deviations from the Lorentz absorption observed in pure CO and in CO-N₂ at low temperature are partially ascribed to the formation of van der Waals dimers.     

ESCA studies of CO2, CS2 and COS

The core level electron spectra of CO₂, CS₂ and COS excited by Mg Kα radiation have been studied to identify shake-up satellite lines associated with ionization from these levels. A number of such lines have been seen and possible assignments have been suggested using the excited states of the molecule as a guide. The valence spectra have also been recorded and they too were found to be rich in shake-up structure. The observed variation of the valence line intensities is discussed and compared with predictions made from an intensity model. The validity of distinguishing between π and σ symmetries in linear molecules in applying the intensity model is confirmed.     

Fine-structure mixing of excited states of cesium atoms upon an impact on the surface of a sapphire single crystal

The spectrum of resonantly excited luminescence of Cs atoms in a microcell with sapphire windows has been studied. Spectral wings of atomic luminescence near the windows have been revealed near (±50 cm^?1) the D2 line of the excited 6S _1/2–6P _3/2 transition. At the same time, the radiation of the D1 line has been found. The features of the spectrum of the far wings, namely, the exponential shape and the relatively small difference between the static and the antistatic wings, as well as the radiation of the D1 line, have been explained by the mixing of fine-structure states due to interactions of Cs atoms with the sapphire windows. From the relative intensity of the lines, it has been determined that the probability of luminescence quenching at the window surfaces differs from unity by no less than 1/700.     

The A-emission of KBr : Tl

The line shapes and relative efficiencies of A_T and A_X emission bands of KBr : Tl have been studied over a wide temperature range (10–500 K). The behavior of A_T and A_X emissions has been described phenomenologically in terms of the coexistence of two different kinds of minima on the adiabatic potential energy surface of the ³T_1u relaxed excited state. The line shape parameters and the A-emission temperature dependence show that T and X minima belong to distortions of different symmetry. A model considering the emission processes from T and X minima separately, in spaces of different distortions, is shown to account well for the experimental results. The emission at very low temperatures (below 50 K) was found to be sensitive to trace impurities.     

Measurements of N2−, O2−, and air-broadened linewidths of ozone in the millimeter region: Temperature dependence of the linewidths

Measurements have been made at room temperature on the widths of selected microwave lines of ozone broadened by three gases: oxygen, nitrogen, and air. For the 2_1,1 ← 2_0,2 line, the temperature dependence of the foreign-gas broadening parameters has been studied in the range 240–293 K. The results are reported along with their accuracies, and are compared with published data.     

Optical emission studies of sulphur plasma using laser induced breakdown spectroscopy

We present the optical emission studies of sulphur (S) plasma generated by the first (1064 nm) and second (532 nm) wavelengths of a Q-switched Nd:YAG laser. The target material was placed in front of laser beam in air at atmospheric pressure. The experimentally observed line profiles of neutral sulphur have been used to extract the electron temperature (T _e ) using the Boltzmann plot method, whereas the electron number density (N _e ) has been determined from the Stark broadening. The electron temperature is calculated by varying, distance from, the target surface along the line of propagation of plasma plume and also by varying the laser irradiance. Beside we have studied the variation of number density as a function of laser irradiance as well as its variation with distance from the target surface. It is observed that electron temperature and electron number density increases as laser irradiance is increased.     

Line parameters of H2O around 0.8 μm studied by tuneable diode laser spectroscopy

The absorption spectrum of H₂O has been extensively studied over the past decades in the near-infrared and visible regions, but there remain significant discrepancies in the 10,000-12,500 cm⁻¹ range even for the most intense lines. We have studied 24 lines of H₂O using an external-cavity diode laser emitting in the 810-830 nm range, in order to measure absolute line intensities as well as air- and self-broadening coefficients. Comparisons were made with values obtained from the HITRAN database and also with other parameters from recent experiments or predicted calculations. It is suggested that neglecting the effects of H₂O collisional narrowing in radiative transfer calculations of the Earth's atmosphere may have a small but significant impact on the radiative budget of the Earth.     

Magnetic phase transitions and the dynamic electric polarization in the LaMn<Subscript>2</Subscript>O<Subscript>5</Subscript> compound

Possible phase transitions to the ferromagnetic phase in the LaMn₂O₃ compound have been studied in the framework of a phenomenological approach based on a symmetry analysis. The conditions that parameters of the thermodynamic potential must satisfy to realize a second-order transition have been found. The line of the first-order phase transitions in this system and the critical point of the second-order phase transition line have been determined. It was shown that a dynamic electric polarization can form in the antiferromagnetic phase.     

Laser-based optical emission studies of barium plasma

We present the optical emission characteristics of the barium plasma produced at the surface of barium hydroxide Ba(OH)₂, also known as baryta, generated by the first harmonic (1,064 nm) of a Q-switched Nd:YAG laser. The laser beam was focused on target material by placing it in air at atmospheric pressure. The experimentally observed line profiles of neutral barium have been used to extract the electron temperature using the Boltzmann plot method, whereas the electron number density has been determined from the Stark broadening. The electron temperature is calculated by varying distance from the target surface along the line of propagation of plasma plume and also by varying the laser energy. Besides, we have studied the variation of number density as a function of laser energy as well as its variation with distance from the target surface. It is observed that electron temperature and electron number density increase as laser energy increases.     

用光伏谱方法研究InGaAs/GaAs应变量子阱的性质

采用低温光伏谱方法，研究了应变In_0.18Ga_0.82/GaAs单量子阱结构中各子能级之间的光跃迁，并与理论计算的结果进行比较，对光伏谱的谱峰跃迁能量随温度变化的分析，表明量子阱中的应变与温度基本无关．研究了光伏谱的谱峰半高宽度随温度的变化关系．讨论了声子关联、混晶组分起伏及生长界面不平整对光伏谱谱峰宽度的影响 关键词：     

Line Broadening and Shifting Studies of the J=5←4 Transition of Carbon Monoxide Perturbed by CO, N2, and O2

The collisional relaxation of the J=5←4 rotational transition of CO induced by carbon monoxide, nitrogen, and oxygen has been studied at room temperature. Pressure-broadening parameters were determined as 3.29(2), 2.61(2), and 2.30(2) MHz/Torr for CO, N₂, and O₂ buffer gases, respectively. Experimental deviations from the Voigt line shape profile have been observed which are mostly the effect of a narrowing in the spectral line core. The difference between the model profile and the experimental profile is less than 0.5% of the maximum line amplitude in the investigated pressure range 0.2-5 Torr. In addition, a small positive collision-induced shift of the line center frequency was observed for the pure gas, corresponding to a pressure self-shift parameter of 6(3) kHz/Torr.     

Internal photoemission and plasmon gain in solid and thin films of Al

Weak features in the electron spectrum of Al excited by bremsstrahlung radiation from a Cu anode have been studied using a recently developed multidetector. A feature at ～1410 eV which has been identified as the Al 2p internal photoelectron line was found to have an intensity 4.2 × 10^?3 times that of the Al KL_2,3L_2,3:¹D₂ Auger line, in agreement with a simple theoretical treatment. The identification of this feature is confirmed by the observation of an ～67% decrease in its intensity in spectra obtained from clean Al films in the thickness range 3.1–34.0 nm. The intensity of a plasmon gain peak at ～1404 eV is found to be independent of thickness for films of thickness greater than 7.5 nm.     

Field electron emission images of multi-walled carbon nanotubes

Field electron emission microscope images from multi-walled carbon nanotubes can typically be characterized by the presence of five pentagons surrounding a sixth central pentagon. The observations of bright line centered interference patterns between adjacent pentagons in the field electron emission microscope images of multi-walled carbon nanotubes have been reported in the literature. We have observed a shift from bright to dark line centered interference patterns and associated this with the presence of surface adsorption. In order to identify the origin of the contaminant, multi-walled carbon nanotubes were dosed with H₂, H₂O, CO and O₂ and then imaged in the field electron emission microscope. Only the samples exposed to O₂ showed a shift from a bright line centered pattern between adjacent pentagons of a clean surface to a dark line centered pattern when one pentagon was contaminated or a bright line centered pattern when both adjacent pentagons become contaminated. The results of the experimental studies and the modeling of the changes in the field emission pattern as phase shifts in the wave function of the tunneling electrons due to modifications in the surface work function are presented.     

Ferromagnetic resonance in arrays of highly anisotropic nanoparticles

We present in this study computational simulations of the ferromagnetic resonance response of magnetic nanoparticles with a uniaxial anisotropy considerably larger than the microwave excitation frequency (in field units). The particles are assumed to be randomly oriented in a two dimensional lattice, and are coupled by dipolar interactions through an effective demagnetization field, which is proportional to the packing fraction. We have included in the model fluctuations in the anisotropy field (H_K) and allowed variations in the demagnetizing field. We then analyzed the line shape and line intensity as a function of both fields. We have found that when H_K is increased the line shape changes drastically, with a structure of two lines appearing at high fields. The line intensity has a maximum when H_K equals the frequency gap and decreases considerably for larger values of the anisotropy. The effects of fluctuations in H_K and variations in the packing fraction have been also studied. Comparison with experimental data shows that the overall observed behavior is dominated by the particles with lower anisotropy.     

Raman study of temperature and pressure effects on vibrational relaxation in liquid CHCl3 and CDCl3

The Raman line shapes of the ν₁(A ₁)C-H and C-D stretching fundamentals in liquid CHCl₃ and CDCl₃ have been measured as a function of pressure from 1 bar to 4·5 kbar within the temperature range 30°C to 90°C. Densities have also been determined under the same experimental conditions. The vibrational relaxation rates are obtained from the isotropic component of the Raman band and the experimental results can be summarized as follows: (i) as T increases at constant density the vibrational relaxation rate increases; (ii) at constant T, the increase in density produces an increase in the relaxation rate; (iii) an increase in temperature at constant pressure results in an increased relaxation rate. The above three cases hold for the CDCl₃ liquid, whereas only (ii) may be stated for the CHCl₃ liquid.

The experimental vibrational data are interpreted in terms of the Kubo stochastic line-shape theory and the collinear-isolated-binary-collision model proposed by Fischer and Laubereau. Application of the Kubo formalism shows that vibrational dephasing is the dominant relaxation mechanism and that the modulation is fast both in liquid CHCl₃ and CDCl₃.

Interpretation in terms of the binary collision dephasing model leads to the following results: (i) the pure dephasing mechanism seems to be the dominant broadening mechanism for the isotropic Raman line shapes studied; (ii) the calculated dephasing rates as a function of density and temperature show agreement with the experimental data. In these calculations the elastic collision times are obtained from the modified Enskog theory.     

Some magnetic properties of Mn(TCNQ)2

The EPR spectra of polycrystalline Mn(TCNQ)₂·3H₂O and Mn(TCNQ?d₄)₂ have been studied as a function of temperature from 1.5 K to 375 K. At very low temperatures the line width indicates an exchange interaction similar to that of other manganese salts. At 77 K and above the line is narrowed and shifted most likely through interaction with the electronic motion. The bulk susceptibility was measured at room temperature. The observed μ_eff=4.66 implies an antiferromagnetic coupling of the manganese ions.