Perpendicular Geometry Research Articles

Alignment effects in two-photon double ionization of H2in femtosecond xuv laser pulses

Triple-differential cross sections for two-photon double ionization of the aligned hydrogen molecule at the equilibrium distance are presented for a central photon energy of 30 eV. The temporal response of the laser-driven molecule is investigated by solving the time-dependent Schr\"odinger equation in full dimensionality using two-center elliptical coordinates and a finite-element discrete-variable-representation approach. The molecular orientation is found to have a strong effect on the emission modes of the two correlated photoelectrons. This molecular effect is most noticeable when the molecular axis and the laser polarization vector are oriented parallel to each other. For intermediate cases between the parallel and perpendicular geometries, the dominant emission modes for two-electron ejection oscillate between those for the two extreme cases. The contributions from different ionization channels are also analyzed in detail. Depending on the emission direction of the reference electron, the interference contributions from the various channels can be constructive or destructive at small alignment angles, while they always contribute constructively to the triple-differential cross sections near the perpendicular geometry.

Ab Initio and DFT Studies of Conformational Properties of Heteroatom Containing Ketene Analogues and Their Comparison with the Related Cyclic Analogues

Minimum‐energy and transition state geometries of 3‐thioxoprop‐2‐enethial, 3‐thioxoacrylaldehyde, 3‐oxoprop‐2‐enethial, 3‐selenoxoprop‐2‐enethial, 3‐thioxoprop‐2‐eneselenal, 3‐selenoxoprop‐2‐eneselenal, 3‐oxoacrylaldehyde, 3‐selenoxoacrylaldehyde and 3‐oxoprop‐2‐eneselenal were calculated using HF, B3LYP and MP2 levels of theory and 6‐31+G* basis set by rotation around the related ‐C‐C‐ single bonds. In all of the above mentioned molecules, the s‐trans conformation was obtained as the most stable conformer with the 180° dihedral angle, apart from 3‐oxoprop‐2‐enethial and 3‐thioxoprop‐2‐eneselenal which their s-cis conformers were appeared more stability than related to s-trans forms. Their perpendicular geometries, with torsional angles approximately 90°, were as transition state for conformational interconversion between the two global minima forms. Cyclic structures all of the above mentioned molecules were unstable than their linear forms.

Perpendicular ferromagnetic resonance measurements of damping and Landég−factor in sputtered (Co2Mn)1−xGexthin films

X-ray diffraction (XRD), magnetometry, and ferromagnetic resonance (FMR) measurements were performed on sputtered thin films of the nominal Heusler alloy (Co${}_{2}$Mn)${}_{1\ensuremath{-}x}$Ge${}_{x}$ with varying Ge content and annealing temperatures. XRD indicates some degree of B2 alloy formation, with strong (110) texturing. FMR measurements were performed in a perpendicular geometry that minimized the contribution of two-magnon scattering to the linewidth. The FMR data indicate a significant increase in linewidth for samples that lack a well-defined (220) peak, presumably as a result of inhomogeneous line broadening. Samples annealed at 200 \ifmmode^\circ\else\textdegree\fi{}C exhibit decreasing Landau--Lifshitz damping with increasing Ge content, while samples annealed at 245 and 300 \ifmmode^\circ\else\textdegree\fi{}C have a nonlinear dependence of linewidth on frequency. The nonlinear component of the linewidth data was successfully fit with a generalized theory of slowly relaxing impurities, originally proposed by Van Vleck and Orbach. The modified theory includes the possibility of transverse coherence during the relaxation process. Magnetometry and FMR spectroscopy results were analyzed in the context of Malozemoff's generalized Slater--Pauling (GSP) theory, with the conclusion that the Ge sites support a significant negative-polarized spin density of several tens of percent. The GSP analysis results were consistent with a more conventional analysis of the spectroscopic $g$-factor that is appropriate for alloys. The proportionality of the strength of the slow-relaxer contribution to the damping suggests that the negatively polarized Ge atoms are acting as the slowly relaxing impurities in question.

Adsorption properties of H2O2 trapped inside a boron phosphide nanotube

The behavior of H2O2 adsorbed inside a [4,4] armchair boron phosphide nanotube (BPNT) was studied by using density functional calculations. Geometry optimizations were carried out at the B3LYP/6-31G* level of theory using the Gaussian 03 suite of programs. We present the nature of the H2O2 interactions inside the nanotube. The interaction between the guest species (H2O2) and the nanotube and the dipole moments of the different geometries are discussed. The results show that the binding energies and the dipole moments of the nanotube depend on the orientation and location of the H2O2 inside the tube. Among the parallel orientation (AT) and perpendicular orientations (PTA and PTP), the PTA and PTP geometries of the H2O2 are unstable whereas the AT-state geometries show stabilization of the guest species inside the BPNT. For AT orientations, the value of the dihedral angle of the H2O2 trapped inside the BPNT in the most stable conformation displays a notable change with respect to free H2O2. Also, with change of tube type, more efficient binding could not be achieved, and only the orientation and location of the H2O2 inside the tube play an important role in determining the binding energy. The polarization of the BPNT in the presence of the guest species in the PT state is higher than that of the AT state. Adsorption of H2O2 in the AT state slightly reduces the energy gap of the pristine BPNTs and slightly increases their electrical conductance.

Photoisomerization around a Fulvene Double Bond: Coherent Population Transfer to the Electronic Ground State?

Photoisomerization around a central fulvene-type double bond is known to proceed through a conical intersection at the perpendicular geometry. The process is studied with an indenylidene-dihydropyridine model compound, allowing the use of visible excitation pulses. Transient absorption shows that 1) stimulated emission shifts to the red and loses oscillator strength on a 50 fs timescale, and 2) bleach recovery is highly nonexponential and not affected by solvent viscosity or methyl substitution at the dihydropyridine ring. Quantum-chemical calculations are used to explain point 1 as a result of initial elongation of the central C=C bond with mixing of S(2) and S(1) states. From point 2 it is concluded that internal conversion of S(1)→S(0) does not require torsional motion to the fully perpendicular state. The S(1) population appears to encounter a sink on the torsional coordinate before the conical intersection is reached. Rate equations cannot model the observed ground-state recovery adequately. Instead the dynamics are best described with a strongly damped oscillatory contribution, which could indicate coherent S(1)-S(0) population transfer.

Structure of Methyl Pyruvate and α-(1-Naphthyl)ethylamine on Pd(111)

The adsorption of methyl pyruvate and α-(1-naphthyl)ethylamine (NEA) on Pd(111) is explored using first-principles density functional theory (DFT) calculations. It is found that methyl pyruvate adsorbs in a flat-lying geometry with a heat of adsorption of ∼44 kJ/mol, in good agreement with the experimentally measured desorption activation energy of 41 ± 6 kJ/mol. For a perpendicular methyl pyruvate geometry, the s-cis conformer is the most stable, while previous experimental results suggest that it adsorbs in the s-trans conformer. Since the s-trans conformer is the most stable in the gas phase, this may be due to the formation of a metastable species on the surface. The calculated heat of adsorption (∼29 kJ/mol) is in good agreement with the experimental desorption activation energy (33 ± 4 kJ/mol). NEA adsorbs on Pd(111) predominantly through the naphthyl ring with a heat of adsorption of ∼224.3 kJ/mol in an exo conformation and 2.1 kJ/mol less stable in an endo conformation. Including effects of van de...

Theoretical study on (e,2e) process for helium in perpendicular geometry

The triple differential cross section for electron impact ionization of helium in the perpendicular geometry is calculated by use of BBK model and modified BBK model. The results of the present work are compared with experimental data. The structure of the cross section is analysed and the exchange effects are discussed systematically.

SO2 Adsorption on Pt(111) and Oxygen Precovered Pt(111): A Combined Infrared Reflection Absorption Spectroscopy and Density Functional Study

We have performed a combined molecular beam (MB)/infrared reflection absorption spectroscopy (IRAS) and density functional (DF) study on the adsorption of sulfur dioxide (SO2) on clean and oxygen precovered Pt(111). The adsorbate species formed as a function of coverage and their structural and chemical transformations upon subsequent annealing were followed systematically by IRAS. It is shown that, upon adsorption on clean Pt(111) at 100 K, SO2 adsorbs molecularly in two geometries. Calculations reveal that these geometries correspond to molecules oriented parallel or perpendicular to the surface. Upon heating up to 250 K, conversion between the two species occurs with the fraction of upright standing SO2 increasing with increasing temperature. Between 300 and 350 K, all surface species desorb without decomposition. This is in sharp contrast to oxygen precovered Pt(111), on which, in addition to the formation of molecular SO2 in flat and perpendicular geometry, partial formation of SO3 is observed even a...

First-principles Study of Field Emissions from Natrium-Encapsulated Boron-Nitride Nanotube in a Perpendicular Geometry

The field emission from pure boron-nitride nanotube and boron-nitride nanotube encapsulated with natrium atoms with the electric field perpendicular to the axis of nanotubes is simulated based on a self-consistent method using the density-functional formalism. It has been found that the nearly-free-electron states in boron-nitride nanotube would perform very well in field emissions after natrium atom encapsulation. The characters of total energy distribution curves are analyzed to seek the function of nearly-free-electron states in the field emission, with special attention to response of the emission current to the external electric field. At last, the perpendicular emission geometry is found to possess a very sensitive response degree which is supposed to be related to specific expansion orientation of the nearly-free-electron states in this system.

Thermally driven spin injection from a ferromagnet into a non-magnetic metal

Creating, manipulating and detecting spin polarized carriers are the key elements of spin based electronics. Most practical devices use a perpendicular geometry in which the spin currents, describing the transport of spin angular momentum, are accompanied by charge currents. In recent years, new sources of pure spin currents, i.e., without charge currents, have been demonstrated and applied. In this paper, we demonstrate a conceptually new source of pure spin current driven by the flow of heat across a ferromagnetic/non-magnetic metal (FM/NM) interface. This spin current is generated because the Seebeck coefficient, which describes the generation of a voltage as a result of a temperature gradient, is spin dependent in a ferromagnet. For a detailed study of this new source of spins, it is measured in a non-local lateral geometry. We developed a 3D model that describes the heat, charge and spin transport in this geometry which allows us to quantify this process. We obtain a spin Seebeck coefficient for Permalloy of -3.8 microvolt/Kelvin demonstrating that thermally driven spin injection is a feasible alternative for electrical spin injection in, for example, spin transfer torque experiments.

C6+-impact ionization of helium in the perpendicular plane: Ionization to the ground state, excitation-ionization, and relativistic effects

In search of the discrepancy between theory and experiment in perpendicular plane geometry for C{sup 6+} ionization of He at 100 MeV/amu, we have used the first and second Born approximations to examine whether ionization to an excited He{sup +} state could be significant, whether relativistic effects could be important, and whether there is substantive sensitivity to the He wave functions used in the calculations. We fail to find any explanation of the discrepancy. Of the three possibilities, only relativistic effects turn out to be significant but then only in changing the overall normalization of the cross section, not in changing its shape, which is a prerequisite to getting agreement with experiment. The second Born calculations are in excellent accord with previous impact parameter coupled pseudostate results [Phys. Rev. A 81, 042704 (2010)] and confirm, yet again, that elastic scattering of the projectile by the target nucleus cannot explain the discrepancy. The calculations are extended to the lower impact energy of 2 MeV/amu. Here, in perpendicular plane geometry, ionization to excited He{sup +} states becomes significant and we find an interesting ''oscillatory'' structure in both the ground- and excited-state cross sections. Comparison is made with some relative experimental data and,more » although the agreement is poor, possibly because of the need to include experimental resolutions, there are nuances in the data that mirror the structures in the calculations.« less

Laser-induced free–free transitions in elastic electron scattering from CO2

This paper presents measurements of laser-induced free–free transitions of electrons scattered from CO2 molecules in the ground electronic state at incident electron energies of 3.8 and 5.8 eV under a pulsed CO2 laser field. The differential cross section of free–free transitions involving absorption and emission of up to two photons was measured at various scattering angles with the polarization of the laser either parallel with or perpendicular to the momentum change vector of the scattered electrons. The results of the parallel geometry are found to be in qualitative agreement with the predictions of the Kroll–Watson approximation within the experimental uncertainty whereas those of the perpendicular geometry show marked discrepancy with the Kroll–Watson predictions.

Theoretical study on photochemical behavior of trans-2-[4′-(dimethylamino)styryl]benzothiazole

Photochemistry of trans-2-[4′-(dimethylamino)styryl]benzothiazole ( t-DMASBT) has been examined theoretically. Ground state calculations are performed by density functional theory (DFT) method. For excited-state calculations restricted configuration interaction singles (RCIS) combined with time dependent DFT (TDDFT) approach was used. Theoretical calculations predicted the existence of two ground state conformers and the photophysics of both the conformers are nearly identical. With torsional rotation of dimethylamino group, the energies of S 1 and S 2 states increase, but that of S 3 state decreases. In contrary to an earlier report [J. Photochem. Photobiol. A: Chem. 195 (2008) 368–377], the calculation predicted at the perpendicular geometry the HOMO is localized on dimethylamino and, HOMO and LUMO are decoupled. Excitation from HOMO to LUMO at perpendicular geometry results in twisted intramolecular charge transfer (TICT) state. Avoided crossing of S 3 and S 1 states causes a barrier for formation of TICT state from locally excited state. Potential energy surface of isomerization constructed by TDDFT method suggests that the photoisomers are formed through phantom state in a nonradiative way, not by a radiative way from cis and trans isomers as proposed earlier by Saha et al. [J. Photochem. Photobiol. A: Chem. 199 (2008) 179–187].

Evidence for the phantom state in photoinduced cis–trans isomerization of stilbene

Abstract Transient absorption spectra of cis-stilbene in solution, recorded in the range 275–690 nm with 80 fs instrument response, reveal two successive evolving bands. One at 630 nm decays on a subpicosecond scale; it corresponds to vertically-excited nearly planar S1 state. The other, growing and decaying band at 340 nm, is shown to be consistent with theoretically predicted phantom state p∗ of perpendicular molecular geometry. The lifetime of p∗ is determined to be τ p ∗ = 0.4 ps in acetonitrile and 0.3 ps in hexane.

Exchange bias in Pt doped NiMn thick films

Magnetization and electron spin resonance (ESR) measurements were carried out on a 1.2 at. % Pt doped NiMn thin film (8000 Å) in the temperature range of 5–200 K for both parallel (field parallel to the film surface) and perpendicular configurations. M versus H loops were recorded at selected temperatures. Magnetization curves in the parallel configuration differ from those in the perpendicular geometry in many respects, including the anisotropy fields derived from these curves, and the coercivity. In addition, the temperature dependences of the magnetization in a small negative field (−0.5 Oe) and several larger positive fields will also be reported. All of these phenomena can be understood by the coexistence of Mn-rich and Mn-deficient aggregated granular regions coupled antiferromagnetically. Furthermore, the exchange stiffness constant (D), bulk anisotropy constant, and surface anisotropy constant were deduced from ESR measurements. The fitted ESR parameters are in good agreement with the behavior deduced from magnetization.

Reconstruction of the electric field in type-II superconducting thin films in perpendicular geometry

The study of electric field distributions induced by flux creep in type-II superconducting films allows for important insight into the mechanism of vortex dynamics, the temporal evolution of flux and current distributions, and the occurrence of local losses. Most studies are based on the assumption that a phenomenological materials law, which has been extracted from macroscopic transport measurements, can be also applied to the local electric field during magnetization decay. We evaluate this ansatz by reconstructing the three-dimensional-induced ${\mathbf{E}}_{i}$ and potential ${\mathbf{E}}_{p}$ electric fields from experimentally measured time dependence of the flux density distribution. The results are quantitatively compared with solutions of the nonlinear and nonlocal equation of motion for the flux penetration, where the Maxwell equations as well as a materials law are utilized to obtain a two-dimensional ${\mathbf{E}}_{i,2\text{D}}$ and ${\mathbf{E}}_{p,2\text{D}}$. We focus our analysis on the electric field distributions on a partially penetrated magnetized state of an epitaxial ${\text{YBa}}_{2}{\text{Cu}}_{3}{\text{O}}_{6.95}$ film.

Coincidence studies of He ionized byC6+,Au24+, andAu53+

A recently developed [Phys. Rev. A 79, 042707 (2009)] impact parameter coupled pseudostate approximation (CP) is applied to calculate triple differential cross sections for single ionization of He by ${\mathrm{C}}^{6+}$, ${\mathrm{Au}}^{24+}$, and ${\mathrm{Au}}^{53+}$ projectiles at impact energies of $100$ and 2 MeV/amu for ${\mathrm{C}}^{6+}$ and $3.6$ MeV/amu for ${\mathrm{Au}}^{24+}$ and ${\mathrm{Au}}^{53+}$. For ${\mathrm{C}}^{6+}$, satisfactory, but not perfect, agreement is found with experimental measurements in coplanar geometry, but there is substantial disagreement with data taken in a perpendicular plane geometry. The CP calculations firmly contradict a projectile-nucleus interaction model which has been used to support the perpendicular plane measurements. For ${\mathrm{Au}}^{24+}$ and ${\mathrm{Au}}^{53+}$, there is a complete lack of accord with the available experiments. However, for ${\mathrm{Au}}^{24+}$ the theoretical position appears to be quite firm with clear indications of convergence in the CP approximation and very good agreement between CP and the completely different three-distorted-waves eikonal-initial-state (3DW-EIS) approximation. The situation for ${\mathrm{Au}}^{53+}$ is different. At the momentum transfers at which the measurements were made, there are doubts about the convergence of the CP approximation and a factor of 2 difference between the CP and 3DW-EIS predictions. The discord between theory and experiment is even greater with the experiment giving cross sections a factor of 10 larger than the theory. A study of the convergence of the CP approximation shows that it improves rapidly with reducing momentum transfer. As a consequence, lower-order cross sections than the triple are quite well converged and present an opportunity for a more reliable test of the experiment.

O-Capped Heteroadamantyl-Substituted Hydrazines and Their Oxidation Products

The mixed valence bishydrazine radical cation 6(+), obtained by oxidation of 2,6-bi-(2'-oxa-6'-azaadamantane-6'-yl)-2,6-diazaadamantane-2,6-diyl (6) with silver or nitrosonium salts, has been prepared and studied. 6 is obtained along with lesser amounts of the trishydrazine, some of the tetrahydrazine, and apparently traces of the pentahydrazine upon reaction of deprotonated 2-oxa-6-azaadamantane with 2,6-dichloro-2,6-diazaadamantane. The EPR spectrum of 6(+) shows that its charge is localized on one hydrazine unit on the EPR time scale. It shows a Hush-type Robin-Day class II mixed valence band in its optical spectrum despite the fact that the nitrogen lone pairs are held in a perpendicular geometry that would lead to no electronic interaction between the nitrogen atoms that are separated by only four sigma bonds if its nitrogens were planar. The electron transfer distance that is estimated from the calculated dipole moment of 6(+) is the same as that obtained using the average distance between the electrons of the triplet state of the dication 6(2+), calculated from its dipolar EPR splitting, as a model for the electron transfer distance of 6(+), 3.7 A. Using Hush's Gaussian approximation for the optical spectrum with this electron transfer distance produces an estimate of the electronic coupling V(ab) through the saturated bridge of about 400 cm(-1), which is consistent with the observed EPR spectrum of 6(+). From the observed dipolar splitting, the trishydrazine diradical dication has its remote hydrazine units oxidized, although the monocation presumably forms at the central hydrazine unit, which lacks substitution by the more electron-withdrawing oxygen atoms.

Structure of a strong supernova shock wave and rapid electron acceleration confined in its transition region

A new rapid energization process within a supernova shock transition region (STR) is reported by utilizing numerical simulation. Although the scale of a STR as a main dissipation region is only several hundreds of thousands km, several interesting structures are found relating to generation of a root of the energetic particles. The nonlinear evolution of plasma instabilities lead to a dynamical change in the ion phase space distribution which associates with change of the field properties. As a result, different types of large-amplitude field structures appear. One is the leading wave packet and another is a series of magnetic solitary humps. Each field structure has a microscopic scale (~ the ion inertia length). Through the multiple nonlinear scattering between these large-amplitude field structures, electrons are accelerated directly. Within a STR, quick thermalization realizes energy equipartition between the ion and electron, hot electrons play an important role in keeping these large-amplitude field structures on the ion-acoustic mode. The hot electron shows non-Maxwellian distribution and could be the seed of further non-thermal population. The "shock system", where fresh incoming and reflected ions are supplied constantly, play an essential role in our result. With a perpendicular shock geometry, the maximum energy of the electron is estimated by equating a width of the STR to a length of the Larmor radius of the energetic electron. Under some realistic condition of M_A = 170 and \omega_{pe}/\Omega_{ce} = 120, maximum energy is estimated to ~ 10 MeV at an instant only within the STR.

Anisotropy evolution of magnetic field fluctuation through the bow shock

Measurement of energy distributions in the wave vector domain reveals how anisotropy of turbulent magnetic field fluctuations evolves as the solar wind encounters the terrestrial bow shock and the magnetosphere. While fluctuations in the solar wind, the magnetosheath, and the magnetospheric cusp regions are characterized by the perpendicular wave vector geometry to the mean magnetic field direction, that in the foreshock region is characterized by the parallel wave vector geometry. Linear and nonlinear plasma processes are discussed for the anisotropy evolution.