Pressure broadening and shift of argon emission lines

Resonance and van der Waals broadening coefficients, as well as width to shift ratios, have been obtained by scanning argon emission lines produced in a high-pressure (～ 1 atm) glow discharge at a temperature of 1130°K. The resonance broadening coefficients yield absolute oscillator strengths of 0·283 ± 0·024 and 0·076 ± 0·008 for the two resonance lines at 1048 Å and 1067 Å. These oscillator strengths are in good agreement with previous measurements. The importance of higher-order terms in the van der Waals potential expansion is demonstrated by the measured coefficients.     

Curves of growth for van der Waals broadened spectral lines

Curves of growth are evaluated for a spectral line broadened by the van der Waals interactions during collisions. The growth of the equivalent widths of such lines is shown to be dependent on the product of the perturber density and the 6/10 power of the van der Waals potential coefficient. When the parameter is small, the widths grow as the 1/2 power of the optical depth as they do for the Voigt profile; but when the parameter is large, they grow as 2/3 power and, hence, faster than the Voigt profile. An approximate analytical expression for the computed growth characteristics is given.     

Relative photodissociation cross-section of NaCs molecule,using argon ion laser lines

Laser-induced photodissociation of NaCs molecule has been observed when a mixture of Na and Cs metal vapour in a glass cell was irradiated by most of the lines of an argon ion laser. The photodissociation results in the 3P state of Na atoms which is correlated with theF ¹Σ⁺ and G¹π molecular states of NaCs. Distribution of photofragments over fine structure components 3² P _3/2 and 3² P _1/2 of Na has been studied. The ratio of intensity ofD ₂ line (5890 Å) toD ₁ line (5896 Å) of Na varies from around 2 at 5145 Å to about 3.5 at 4579 Å. The relative photodissociation cross-section increases monotonically as the wave-length of laser light decreases from 5145 Å to 4579 Å. It is seen that the 4579 Å photon is about 200 times more effective than the 5145 Å photon in causing the photoreaction NaCs + (Ar⁺ photon) → Na*(3P) + Cs(6S).     

Studium der van der Waals-Kraft im Bereich kleiner Abstände

The theory of Dzyaloshinskii allows us to calculate the van der Waals force acting between two surfaces which are held at a distance of 10⁴ Å and less. This calculation was based on the experimentally determined absorption data of quarz. The deflection of a thin quarz plate which was supported at one end with a vaporized bar has been measured to verify the theoretical results. Within the range of accuracy a fair agreement could be reached.     

Measurement of the Stark broadening parameters of some singly ionized argon lines

Half-widths of fifteen Stark broadened argon II lines have been measured in argon plasma behind the reflected shock wave produced in an electromagnetically driven “T” tube. The plasma electron density was determined by the laser interferometry at three different wavelengths, while the plasma temperature was measured from relative intensities of A II lines. Temperatures were in the range 8,500–16,500 °K; electron densities varied from 1.82 to 3.94 · 10¹⁷ cm^?3. The measured A II linewidths are compared with theoretical and other experimental results. It is shown that a) the broadening of A II lines is in good agreement with the theory, b) line broadening increases linearly with electron density, and c) the Stark broadened lines follow the dispersion profile to the distance of at least three halfwidths from the line center.     

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.     

The generalised Huggins-Mayer form of born repulsive potentials for NaCl-type alkali halides

The generalised Huggins-Mayer form of Born repulsive potentials for NaCl-type alkali halides have been re-evaluated using more reliable, recently published thermodynamic data and van der Waals energy coefficients. As with older versions of these potentials excellent agreement between model and experimental values of interionic distance and cohesive energy is achieved. Further, the earlier shortcomings in the failure of the stability condition and predicted elastic constants are significantly reduced. For the majority of salts the new short-range interactions have stronger van der Waals attractions and slider repulsions. The model gives average crystal radii for the alkali ions about ~0.3 Å larger than traditional free ion radii and ~0.08 Å larger than Tosi-Fumi crystal radii. The predicted halogen crystal radii are correspondingly smaller by the same amounts.     

Pressure broadening and shift of the first diffuse series doublet of indium due to the presence of helium and argon

The shift and half-width of In λ 3039 and In λ3256 was measured in Ar and He under pressures up to one thousand p.s.i. The temperature of the absorption tube was 850°C for In λ 3039 and 930°C for In λ 3256. The van der Waals interaction constant for In/Ar was found to be 1·5 x 10^-30 and 8·6 x 10^-31 cm⁶/sec for In λ 3039/Ar and In λ 3256/Ar respectively. In λ 3256 exhibited a small red shift in He for the range of r.d. (from 1 to 16) of He employed.     

Relaxation rates of 69Ga and 71Ga nuclei in aqueous solutions

Line widths in the ⁶Li, ⁷Li, ²³Na, ³⁹K, ⁸⁵Rb, ⁸⁷Rb and ¹³³Cs N.M.R. spectra of solutions of the alkali salts of biphenyl and fluorenone are reported as a function of solvent and temperature. From a numerical analysis of the room temperature data the contribution of the various relaxation mechanisms to the line widths are established. It is shown that the results are consistent with the observed solvent and temperature dependence of the line widths. Values of the electron spin correlation time are obtained and a value of 1·6 ± 0·4 Å is found for the ‘Van der Waals radius’ of the biphenyl anion. Line width expressions for the static and the dynamic ion pair model are presented. It is demonstrated that the static ion pair model applies to solutions of caesium biphenylide. Semi-empirical rules are presented concerning the importance of various relaxation mechanisms for the different alkali nuclei in the type of solution studied here.     

Van der Waals broadening of argon absorption lines

Van der Waals broadening coefficients for Ar absorption lines have been measured using the resonant Faraday effect. These coefficients have the values of 2·9 ± 0·8, 2·4 ± 0·3, 1·9 ± 0·2 (in units of 10^?20 cm^?1 ?cm^?3) for the lines 6965 Å, 7067 Å, 7635 Å and 8115 Å, respectively, respectively. The measured coefficients are in reasonable agreement with measurements carried out on Ar emission lines and with theoretical calculations.     

Messung der Anisotropie der van der Waals-Kraft

As is well known, van der Waals forces between two atoms (not both in an S-state) have no spherical symmetry. We report on an experiment, which verifies this anisotropy by measuring it. The experiment consists in comparing the total scattering cross sections of Ga atoms in selected magnetic substatesm _J=1/2 and 3/2 of the upper (² P _3/2) level of the ground state doublet of Ga. Rare gases are used as the scatterer. The relative total cross section difference in units of 10^?4 is 94.9±4.3 for Xe, 79.4±6.6 for Ar, and 195±5 for He as the scattering gas. In addition, measurements of the total scattering cross sections of Na and Ga on various gases have been made. The apparatus uses an atomic beam with magnetic selection, a common geometry, and a common detecting scheme for both states, which are compared in short intervalls by merely switching the selecting magnet's current. By converting the beam intensity to a pulse rate and summing the numbers of pulses in scalers, the sequence of alternate measurements could be automatized. In that way a comparison could be made every second, thus largely eliminating most drifts, which otherwise would have made impossible an intensity measurement of that accuracy. A theoretical estimate of the experimental results has been made on the following basis: 1. Only van der Waals forces are taken into account. 2. Matrix element sums in the expression for the van der Waals potential are approximately reduced to terms involving only the polarizability of the rare gases and matrix elements of Ga, which can be calculated from Hartree-Fock functions. 3. The Schiff approximation is used to calculate the scattering cross section. The calculations are in rough agreement with experiments, and errors are discussed.     

Interpretation of rare-gas-induced broadening of Rydberg series lines

Approximate expressions have been derived for the cross-sections of rare-gas-induced broadening of the Rydberg series lines on the basis of the interatomic potential which is expressed as a combination of the van der Waals potential, the Fermi potential and the polarization potential. Only the effect of elastic scattering has been taken into account. Multichannel (two-channel) quantum defect theory has been combined with the broadening theory to include the effect of the mutual interaction of the Rydberg series. The resulting cross-sections are in reasonable agreement with the experimental values obtained for Na by Kachru et al. and for Ca and Ba by Ueda et al.     

High density measurements of the Stark broadened profile of the He(II)4686 Å line

The Stark broadened profile of the He(II)4686 Å line has been scanned in the electron density range of 1–3 × 10¹⁸ cm^-3. The electron temperature, as determined from the line to continuum ratio, ranged from 9.4 to 19.9 eV. The plasma which emitted the He(II)4686 Å line was created in a 60-kJ theta pinch operated with a high fill pressure (3 and 5 torr) of pure helium. Electron densities were calculated from the half-half widths of the He(II)4686 Å line using two Stark broadening theories. These electron densities are compared with the electron densities determined from the absolute value of the continuum intensity and a total sweep up compressional model. The two theoretical models predict electron densities in good agreement with the electron densities from the absolute value of the continuum intensity.     

Infra-red spectrum,structure and properties of the N2-Ar van der Waals molecule

The first spectroscopic observation of bound N₂-Ar van der Waals molecules has been achieved with a cryogenic long path cell maintained at 87 K. The infra-red spectrum exhibits prominent fine structure near the N₂ stretching frequency which is assigned to hindered internal rotation of N₂ within the weakly bound complex. An analysis of this fine structure yields a T-shaped equilibrium geometry in which the N₂ bond axis is perpendicular to the N₂-Ar van der Waals bond axis. The observed spectrum is shown to be consistent with an internal rotational barrier of 20 cm^-1 (57 cal/mole). Approximately 20 per cent of the bound species are trapped by this rotational barrier and acquire a locked semi-rigid structure. The remaining 80 per cent have ill-defined geometry and undergo hindered internal rotation. The rotational envelope of an infra-red fundamental is analysed to give an estimate of the N₂-Ar bond length as 3·9 Å.     

Band alignment in SiC-based one-dimensional van der Waals homojunctions

The density functional theory method is utilized to verify the electronic structures of SiC nanotubes (SiCNTs) and SiC nanoribbons (SiCNRs) one-dimensional (1D) van der Waals homojunctions (vdWh) under an applied axial strain and an external electric field. According to the calculated results, the SiCNTs/SiCNRs 1D vdWhs are direct semiconductors with a type-II band alignment and robust electronic structures with different diameters or widths. Furthermore, the SiCNTs/SiCNRs 1D vdWhs are direct semiconductors with a type-I band alignment, respectively, in a range of[-0.3, -0.1] V/Å and[0.1, 0.3] V/Å and change into metal when the electric field intensity is equal to or higher than 0.4 V/Å. Interestingly, the SiCNTs/SiCNRs 1D vdWhs have robust electronic structures under axial strain. These findings demonstrate theoretically that the SiCNTs/SiCNRs 1D vdWhs can be employed in nanoelectronics devices.     

Adsorption configurations of carbon monoxide on gold monolayer supported by graphene or monolayer hexagonal boron nitride: a first-principles study

Using density functional theory with a semiempirical van der Waals approach proposed by Grimme, the adsorption behavior of carbon monoxide on a gold monolayer supported by graphene or monolayer hexagonal boron nitride has been investigated. Based on the changes in the Dirac cone of graphene and a Bader charge analysis, we observe that the Au(111) monolayer gains a small charge from graphene and monolayer h-BN. The adsorbed CO molecule adopts similar adsorption configurations on Au(111)/graphene and Au(111)/h-BN with Au-C distance 2.17?2.50 Å and Au-C-O angle of 123.9°–139.6°. Moreover, we found that for low CO coverages, bonding to the gold surface is surprisingly energy-favorable. Yet the CO adsorption binding energy diminishes at high coverage due to the repulsive van der Waals interactions between CO molecules.     

Influence of complexation and solid environment on the vibrational coherence of DCl

The vibrational dynamics of DCl molecules embedded in different cryogenic matrices is studied by time resolved infrared Degenerate Four Wave Mixing experiments using the infrared free electron laser CLIO. The coherence behaviour of the D-Cl stretch in pure argon as well as in mixed argon/nitrogen van der Waals solids is investigated. Different interactions between the excited molecules and their environment are probed: the van der Waals interaction between the trapped molecules and the solid lattice and the interaction binding complexes trapped in the matrix (either the vdW interaction between DCl and nitrogen or weak H bonds in (DCl)_n clusters). The dependence of the dephasing time on the solid and on specific interactions is clearly observed.     

Über die Wechselwirkung zweier Heliumatome

The interaction energy between two helium atoms in the ground state is calculated by a variational principle. Besides the valence energy 387·exp(?4,42R) (R in Å, energy in eV) and the van der Waals energy ?0,58/R ^5,9 an additional energy term 366·exp(?7,15R) is obtained which is particularly important forR?3 Å. A potential minimum but no equilibrium exists because the zero point energy is too large. The results of other authors are discussed and compared.