Low-Energy Nondipole Effects in Molecular Nitrogen Valence-Shell Photoionization

Observations are reported for the first time of significant nondipole effects in the photoionization of the outer-valence orbitals of diatomic molecules. Measured nondipole angular-distribution parameters for the 3sigmag, 1piu, and 2sigmau shells of N2 exhibit spectral variations with incident photon energies from thresholds to ~200 eV which are attributed via concomitant calculations to particular final-state symmetry waves arising from (E1)[direct-product](M1,E2) radiation-matter interactions first-order in photon momentum. Comparisons with previously reported K-edge studies in N2 verify linear scaling with photon momentum, accounting in part for the significantly enhanced nondipole behavior observed in inner-shell ionization at correspondingly higher momentum values in this molecule

Electric-octupole and pure-electric-quadrupole effects in soft-x-ray photoemission

Second-order [O(k^2), k=omega/c] nondipole effects in soft-x-ray photoemission are demonstrated via an experimental and theoretical study of angular distributions of neon valence photoelectrons in the 100--1200 eV photon-energy range. A newly derived theoretical expression for nondipolar angular distributions characterizes the second-order effects using four new parameters with primary contributions from pure-quadrupole and octupole-dipole interference terms. Independent-particle calculations of these parameters account for a significant portion of the existing discrepancy between experiment and theory for Ne 2p first-order nondipole parameters.Comment: 4 pages, 3 figure

Dipole and nondipole photoionization of molecular hydrogen

We describe a theoretical approach to molecular photoionization that includes first-order corrections to the dipole approximation. The theoretical formalism is presented and applied to photoionization of H_2 over the 20- to 180-eV photon energy range. The angle-integrated cross section σ, the electric dipole anisotropy parameter β_e, the molecular alignment anisotropy parameter β_m, and the first-order nondipole asymmetry parameters γ and δ were calculated within the single-channel, static-exchange approximation. The calculated parameters are compared with previous measurements of σ and β_m and the present measurements of β_e and γ+3δ. The dipole and nondipole angular distribution parameters were determined simultaneously using an efficient, multiangle measurement technique. Good overall agreement is observed between the magnitudes and spectral variations of the calculated and measured parameters. The nondipole asymmetries of He 1s and Ne 2p photoelectrons were also measured in the course of this work

Effect of alkali treatment of lower concentrations on the structure and tensile properties of Pakistan’s coarse cotton fibre

Cotton fibres of high Micronaire values are known to have inferior spinning performance. Either reduction of fibres’ fineness or increase in tensile strength is generally expected to improve the spinnability of fibres. In this piece of research, the effects of alkali treatment at lower concentrations (0.75–2.25M) and higher temperatures (70–100 °C) on the cross-section of cotton fibre and on the tensile strength have been investigated. Observations were made using scanning electron microscopy (SEM) and single fibre tensile strength testing. It was found that the roundness of the fibre cross section was improved and the tensile strength of the fibres also increased after treatment with alkali at lower concentration (0.75 M) and relatively lower temperature (70 °C). It is proposed that such changes occurred due to possible cellulose dissolution/transformations. It was thus concluded that the alkali treatment of cotton fibres at lower concentrations (0.75 M) and 70 °C for a shorter period of time (45 mins) could lead to improvement in tensile strength and roundness of fibre cross-section, thereby improving micronaire

Strong-field control of x-ray absorption

Strong optical laser fields modify the way x rays interact with matter. This allows us to use x rays to gain deeper insight into strong-field processes. Alternatively, optical lasers may be utilized to control the propagation of x rays through a medium. Gas-phase systems are particularly suitable for illustrating the basic principles underlying combined x-ray and laser interactions. Topics addressed include the impact of spin-orbit interaction on the alignment of atomic ions produced in a strong laser field, electromagnetically induced transparency in the x-ray regime, and laser-induced alignment of molecules.Comment: 8 pages, 5 figures, 1 table, LaTe

Kinetic Analysis of Cellulose Acetate/Cellulose II Hybrid Fiber Formation by Alkaline Hydrolysis

Cellulose acetate (CA) can be converted to cellulose II through a deacetylation process using ethanolic NaOH solution. Infrared spectroscopy was used to observe the degree of acetylation by comparing the absorption intensities of C═O and C–O stretches. Attenuated total reflection-Fourier transform infrared (ATR-FTIR) analysis, which only measures a few microns into the fiber diameter, was compared with FTIR, which measures the whole fiber cross-section. Steady deacetylation of the whole fiber over 180 min was observed with FTIR to eventual complete deacetylation. In comparison, ATR-FTIR shows deacetylation occurring more rapidly to complete deacetylation after 90 min, indicating rapid deacetylation of the CA fiber periphery. Data were fitted to a pseudo-second order kinetic model, with high correlation (R² > 0.99), and it was observed that the deacetylation rate (k₂) observed with ATR-FTIR (−0.634 min⁻¹) was twice as rapid as the deacetylation rate observed with FTIR (−0.315 min⁻¹). IR observations were in agreement with the analysis of fiber cross-sections by confocal microscopy, where it was observed that changes in fiber morphology occurred with treatment time and progressive hydrolysis of cellulose acetate to cellulose II. A differential fiber chemical composition was created within the CA fiber cross-section; after 5 min, the outer regions of the fiber cross-section are hydrolyzed to cellulose II and this hydrolysis increases heterogeneously with time to complete hydrolysis after 180 min and conversion to cellulose II. These results indicate the potential to produce fibers with a differential periphery/core structure, which can be accurately designed according to the relative degrees of cellulose II/CA required for specific applications by varying the treatment time in application of this model