65 research outputs found
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
Correlation structure in nondipole photoionization
The nondipole parameters that characterize the angular disribution of the
photoelectrons from the 3d subshell of Cs are found to be altered qualitatively
by the inclusion of correlation in the form of interchannel coupling between
the and photoionization channels. A prominent
characteristic maximum is predicted only in the parameters for
photoionization, while the effect for is rather weak. The results
are obtained within the framework of the Generalized Random Phase Approximation
with Exchange (GRPAE), which in addition to the RPAE effects takes into account
the rearrangement of all atomic electrons due to the creation of a 3d vacancy
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 Ï, the electric dipole anisotropy parameter ÎČ_e, the molecular alignment anisotropy parameter ÎČ_m, and the first-order nondipole asymmetry parameters Îł and ÎŽ were calculated within the single-channel, static-exchange approximation. The calculated parameters are compared with previous measurements of Ï and ÎČ_m and the present measurements of ÎČ_e and Îł+3ÎŽ. 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
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
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 CâO and CâO 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 (RÂČ > 0.99), and it was observed that the deacetylation rate (kâ) observed with ATR-FTIR (â0.634 minâ»Âč) was twice as rapid as the deacetylation rate observed with FTIR (â0.315 minâ»Âč). 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
Whole proteome analyses on Ruminiclostridium cellulolyticum show a modulation of the cellulolysis machinery in response to cellulosic materials with subtle differences in chemical and structural properties
Lignocellulosic materials from municipal solid waste emerge as attractive resources for anaerobic digestion biorefinery. To increase the knowledge required for establishing efficient bioprocesses, dynamics of batch fermentation by the cellulolytic bacterium Ruminiclostridium cellulolyticum were compared using three cellulosic materials, paper handkerchief, cotton discs and Whatman filter paper. Fermentation of paper handkerchief occurred the fastest and resulted in a specific metabolic profile: it resulted in the lowest acetate-to-lactate and acetate-to-ethanol ratios. By shotgun proteomic analyses of paper handkerchief and Whatman paper incubations, 151 proteins with significantly different levels were detected, including 20 of the 65 cellulosomal components, 8 non-cellulosomal CAZymes and 44 distinct extracytoplasmic proteins. Consistent with the specific metabolic profile observed, many enzymes from the central carbon catabolic pathways had higher levels in paper handkerchief incubations. Among the quantified CAZymes and cellulosomal components, 10 endoglucanases mainly from the GH9 families and 7 other cellulosomal subunits had lower levels in paper handkerchief incubations. An in-depth characterization of the materials used showed that the lower levels of endoglucanases in paper handkerchief incubations could hypothetically result from its lower crystallinity index (50%) and degree of polymerization (970). By contrast, the higher hemicellulose rate in paper handkerchief (13.87%) did not result in the enhanced expression of enzyme with xylanase as primary activity, including enzymes from the xyl-doc cluster. It suggests the absence, in this material, of molecular structures that specifically lead to xylanase induction. The integrated approach developed in this work shows that subtle differences among cellulosic materials regarding chemical and structural characteristics have significant effects on expressed bacterial functions, in particular the cellulolysis machinery, resulting in different metabolic patterns and degradation dynamics.This work was supported by a grant [R2DS 2010-08] from Conseil Regional d'Ile-de-France through DIM R2DS programs (http://www.r2ds-ile-de-france.com/). Irstea (www.irstea.fr/) contributed to the funding of a PhD grant for the first author. The funders provided support in the form of salaries for author [NB], funding for consumables and laboratory equipment, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. Omics Services provided support in the form of salaries for authors [VS, MD], but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors [NB, VS, MD] are articulated in the 'author contributions' section.info:eu-repo/semantics/publishedVersio
Probing Molecular Shape. 1. Conformational Studies of 5-Hydroxyhexahydropyrimidine and Related Compounds
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