Proposal of an experiment for discovery and study of diffracted radiation of channeled electrons

It is discussed whether it is possible to discover the diffracted radiation of channeled electrons experimentally. A new method for orienting a crystal in average-energy electron accelerators with short times of the acceleration cycle and the electron spill to the target (microtrons and linear accelerators) is proposed. It uses the integral characteristics of the yield of soft radiation from thin metal targets and provides a considerable decrease in the time required for the crystal orientation. An experimental setup is created, a complex of programs for equipment operation is developed and debugged, and test measurements are conducted at the microtron operating at the Institute of Nuclear Physics of Moscow State University, which makes it possible to carry out proposed experimental studies in the nearest future.     

Ultraviolet photodissociation of the van der Waals dimer (CH3I)2 revisited. II. Pathways giving rise to neutral molecular iodine

The formation of neutral I2 by the photodissociation of the methyl iodide dimer, (CH3I)2, excited within the A band at 249.5 nm is evaluated using velocity map imaging. In previous work [J. Chem. Phys. 122, 204301 (2005)], we showed that the formation of I2+ from photodissociation of the methyl iodide dimer takes place via ionic channels (through the formation of (CH3I)2+). It is thus not possible to detect neutral I2 by monitoring I2+. Neutral I2 is detected in this study by monitoring I atoms arising from the photodissociation of I2. Iodine atoms from I2 photodissociation have a characteristic kinetic energy and angular anisotropy, which is registered using velocity map imaging. We use a two-color probe scheme involving the photodissociation of nascent I2 at 499 nm, which gives rise to I atoms that are ionized by (2+1) resonance enhanced multiphoton ionization at 304.67 nm. Our estimate of the yield of nascent I2 is based on the comparison with the signal from I2 at a known concentration. Using molecular beams with a small fraction of CH3I (1% in the expanded mixture) where smaller clusters should prevail, the production of I2 was found to be negligible. An upper estimate for the quantum yield of I2 from (CH3I)2 dimers was found to be less than 0.4%. Experiments with a higher fraction of CH3I (4% in the expanded mixture), which favor the formation of larger clusters, revealed an observable formation of I2, with an estimated translational temperature of about 820 K. We suggest that this observed I2 signal arises from the photodissociation of several CH3I molecules in the larger cluster by the same UV pulse, followed by recombination of two nascent iodine atoms is responsible for neutral I2 production.     

Evaluation of surface tension and Tolman length as a function of droplet radius from experimental nucleation rate and supersaturation ratio: metal vapor homogeneous nucleation

Zinc and silver vapor homogeneous nucleations are studied experimentally at the temperature from 600 to 725 and 870 K, respectively, in a laminar flow diffusion chamber with Ar as a carrier gas at atmospheric pressure. The size, shape, and concentration of aerosol particles outcoming the diffusion chamber are analyzed by a transmission electron microscope and an automatic diffusion battery. The wall deposit is studied by a scanning electron microscope (SEM). Using SEM data the nucleation rate for both Zn and Ag is estimated as 10(10) cm(-3) s(-1). The dependence of critical supersaturation on temperature for Zn and Ag measured in this paper as well as Li, Na, Cs, Ag, Mg, and Hg measured elsewhere is analyzed. To this aim the classical nucleation theory is extended by the dependence of surface tension on the nucleus radius. The preexponent in the formula for the vapor nucleation rate is derived using the formula for the work of formation of noncritical embryo [obtained by Nishioka and Kusaka [J. Chem. Phys. 96, 5370 (1992)] and later by Debenedetti and Reiss [J. Chem. Phys. 108, 5498 (1998)]] and Reiss replacement factor. Using this preexponent and the Gibbs formula for the work of formation of critical nucleus the dependence of surface tension on the radius R(S) of the surface of tension is evaluated from the nucleation data for above-mentioned metals. For the alkali metals and Ag the surface tension was determined to be a strong function of R(S). For the bivalent metals (Zn, Hg, and Mg) the surface tension was independent of radius in the experimental range. A new formula for the Tolman length delta as a function of surface tension and radius R(S) is derived by integration of Gibbs-Tolman-Koenig equation assuming that delta is a monotonic function of radius. The formula derived is more correct than the Tolman formula and convenient for the elaboration of experimental data. Using this formula the values of delta are determined as a function of R(S) from the experimental nucleation data. It is determined that all the metals considered are characterized by strong dependence of delta on radius; for the bivalent metals delta changes sign.     

Disorder-induced inhomogeneities of the superconducting state close to the superconductor-insulator transition

Scanning tunneling spectroscopy at very low temperatures on homogeneously disordered superconducting titanium nitride thin films reveals strong spatial inhomogeneities of the superconducting gap Delta in the density of states. Upon increasing disorder, we observe suppression of the superconducting critical temperature Tc towards zero, enhancement of spatial fluctuations in Delta, and growth of the Delta/Tc ratio. These findings suggest that local superconductivity survives across the disorder-driven superconductor-insulator transition.     

Shortened equations for the elliptically polarized wave

The field of an elliptically polarized wave is represented for the convenient solution of practical problems. The wave amplitude is written in terms of four parameters: magnitude E, phase φ, angle ψ of the polarization plane, and ellipticity ? (|?| is the ratio of the ellipse axes). The shortened equations are derived using these parameters and the solution of the shortened equations is obtained for a linear medium.     

Polarization effects at two-beam interaction on reflection holographic gratings in sillenite crystals

The polarization structure of the signal wave that interacts with a circularly polarized pump wave on the reflection holographic gratings in the (112)-, (111)-, and (110)-cut Bi₁₂TiO₂₀ (BTO) crystals is experimentally and theoretically analyzed. An analytical expression for the vector field of the signal wave that is valid for an arbitrary orientation of the cubic refractive crystal is derived using approximation of the nondepleting circularly polarized pump wave. The contribution of the absorption component of the reflection hologram into the counter interaction is estimated for the crystals under study using the approximation of the experimental data with theoretical curves. Based on the experiments with incoherent quasi-monochromatic radiation, it is demonstrated that the real BTO crystals exhibit weak induced linear birefringence.     

Concerning the shift of nonlinear optical resonances in a magnetic field

The shift of components of the magnetic hyperfine structure (MHS) of a vibrational-rotational molecular transition in a weak magnetic field is explored. The numerical data are given for the methane transition at λ=3.39 μm [theF ₂ ⁽²⁾ component of theP(7) line of thev ₃ band]. The shift of the line contour due to the magnetic field is found when the MHS components overlap.     

A lineshape of the trapped particle in anharmonic potential

The line of resonance absorption of an atom in a gas usually suffers Doppler broadening. It has been first shown that the particle trapped in an anharmonic potential emits a narrow line with no Doppler broadening.     

Superconductivity of strongly correlated electrons in copper and ruthenium oxides within the t-J-I model

We propose a t-J-I model with direct ferromagnetic exchange I to explain the superconductivity of copper oxides and the ruthenate Sr₂RuO₄ on the basis of the analysis of the electronic structure of these substances. We analyze the possible p-and d-type superconducting solutions. Solutions of the s type with singlet pairings are impossible in the strong-electron-correlations regime, and p-type solutions correspond to triplet superconductivity and is formed near the ferromagnetic instability threshold in ruthenates. The solution with the symmetry near the antiferromagnetic instability threshold corresponds to copper oxides. We also discuss the reason for the high values of the superconducting transition temperature (T _c ∼100 K) in copper oxides and the low values (T _c ∼1 K) in ruthenates. Zh. éksp. Teor. Fiz. 116, 655–670 (August 1999)