Energy Dependence Of Cross Section Research Articles

Wavelength-dependent nonsequential double ionization of magnesium by intense femtosecond laser pulses

We report on a systematic investigation of wavelength scaling strong-field double ionization of Mg in intense laser fields. A significant decrease of nonsequential double ionization (NSDI) yield with increasing wavelength from 800--2000 nm is observed. Our data is well reproduced by a three-dimensional Monte Carlo simulation considering recollision impact excitation cross section. We demonstrate that the NSDI of Mg mainly occurs via the first ionic excited state ${\mathrm{Mg}}^{+*}(3p\phantom{\rule{0.16em}{0ex}}^{2}P_{3/2,1/2})$ pumped by returning electron impact process. The recollision impact direct ionization pathway plays a minor role here. The wavelength dependence of the NSDI ratio is due to the recollision energy-dependent excitation cross section as well as the electron wave packet diffusion effects, both sensitively depending on the wavelength. Our work represents a step towards strong-field double ionization experiments on Mg in the long wavelength limit and sheds light on the NSDI mechanism of alkaline-earth metal atoms.

Coherence length of neutrino oscillations in a quantum field-theoretical approach

We consider a novel quantum field-theoretical approach to the description of processes passing at finite space-time intervals based on the Feynman diagram technique in the coordinate representation. The most known processes of this type are neutrino and neutral kaon oscillations. The experimental setting of these processes requires one to adjust the rules of passing to the momentum representation in the Feynman diagram technique in accordance with it, which leads to a modification of the Feynman propagator in the momentum representation. The approach does not make use of wave packets, both initial and final particle states are described by plane waves, which simplifies the calculations considerably. We consider neutrino oscillation processes, where the neutrinos are produced in three-particle weak decays of nuclei and detected in the charged-current interaction with nuclei or in the charged- and neutral-current interactions with electrons. Particular examples are considered and it is shown that the momentum spread of the produced neutrinos and the energy dependence of the differential cross section of the detection process result in the suppression of neutrino oscillation, which is characterized by a coherence length specific for a pair of production and detection processes. This coherence length turns out to be much less than the coherence length in the standard quantum-mechanical approach defined by the quantum uncertainty of neutrino momentum.

Neutron capture cross-section measurement and resolved resonance analysis of 237Np

ABSTRACTThe neutron capture cross-section of 237Np has been measured in the neutron energy region from 10 meV to 500 eV. A neutron time-of-flight method was employed using the NaI(Tl) spectrometer in the ANNRI beamline at the Japanese Proton Accelerator Research Complex (J-PARC). The experimental capture yield was derived using the pulse-height weighting technique and an energy-dependent cross-section was obtained relative to the incident neutron spectrum derived from a 10B(n, )7Li reaction yield. The absolute cross-section was determined by normalizing the results to JENDL-4.0 cross-section data at the first resonance of 237Np. The thermal cross-section was measured to be 177.6 ± 3.8 b. The resolved resonance region was analyzed with the REFIT code. An average radiation width = 40.3 ± 0.5 meV, a mean level spacing D0 = 0.60 ± 0.02 eV and a neutron strength function 104S0 = 1.02 ± 0.12 were obtained.

Energy-Dependent Relative Cross Sections in Carbon 1s Photoionization: Separation of Direct Shake and Inelastic Scattering Effects in Single Molecules.

We demonstrate that the possibility of monitoring relative photoionization cross sections over a large photon energy range allows us to study and disentangle shake processes and intramolecular inelastic scattering effects. In this gas-phase study, relative intensities of the carbon 1s photoelectron lines from chemically inequivalent carbon atoms in the same molecule have been measured as a function of the incident photon energy in the range of 300-6000 eV. We present relative cross sections for the chemically shifted carbon 1s lines in the photoelectron spectra of ethyl trifluoroacetate (the "ESCA" molecule). The results are compared with those of methyl trifluoroacetate and S-ethyl trifluorothioacetate as well as a series of chloro-substituted ethanes and 2-butyne. In the soft X-ray energy range, the cross sections show an extended X-ray absorption fine structure type of wiggles, as was previously observed for a series of chloroethanes. The oscillations are damped in the hard X-ray energy range, but deviations of cross-section ratios from stoichiometry persist, even at high energies. The current findings are supported by theoretical calculations based on a multiple scattering model. The use of soft and tender X-rays provides a more complete picture of the dominant processes accompanying photoionization. Such processes reduce the main photoelectron line intensities by 20-60%. Using both energy ranges enabled us to discern the process of intramolecular inelastic scattering of the outgoing electron, whose significance is otherwise difficult to assess for isolated molecules. This effect relates to the notion of the inelastic mean free path commonly used in photoemission studies of clusters and condensed matter.

Entrance-channel dynamics in the reaction 40Ca+208Pb

The entrance-channel dynamics including capture, fusion, and quasifission processes for the reaction $^{40}$Ca+$^{208}$Pb is investigated in the fully microscopic time-dependent Hartree-Fock (TDHF) theory.The calculations are performed in three-dimensional Cartesian coordinate without any symmetry restrictions, in which the full Skyrme energy functional SLy4d and SLy5 are adopted.We study the energy dependence of capture cross sections, and find that the experimental data are well reproduced by the TDHF calculations. Both fusion and quasifission events are observed in the reaction $^{40}$Ca+$^{208}$Pb. The contact time, mass and charge of quasifission fragments show a wide distribution in SLy4d compared withSLy5, implying that more nucleons are transferred in the SLy4d calculations.We find that the total kinetic energy of quasifission fragments in the TDHF calculations is distributed around Viola systematics,indicating that most of the relative kinetic energy is dissipated in quasifission dynamics.

Clustered DNA Damages induced by 0.5 to 30 eV Electrons

Low-energy electrons (LEEs) of energies ≤30 eV are generated in large quantities by ionizing radiation. These electrons can damage DNA; particularly, they can induce the more detrimental clustered lesions in cells. This type of lesions, which are responsible for a large portion of the genotoxic stress generated by ionizing radiation, is described in the Introduction. The reactions initiated by the collisions of 0.5–30 eV electrons with oligonucleotides, duplex DNA, and DNA bound to chemotherapeutic platinum drugs are explained and reviewed in the subsequent sections. The experimental methods of LEE irradiation and DNA damage analysis are described with an emphasis on the detection of cluster lesions, which are considerably enhanced in DNA–Pt–drug complexes. Based on the energy dependence of damage yields and cross-sections, a mechanism responsible for the clustered lesions can be attributed to the capture of a single electron by the electron affinity of an excited state of a base, leading to the formation of transient anions at 6 and 10 eV. The initial capture is followed by electronic excitation of the base and dissociative attachment—at other DNA sites—of the electron reemitted from the temporary base anion. The mechanism is expected to be universal in the cellular environment and plays an important role in the formation of clustered lesions.

Transport coefficients for multicomponent gas of hadrons using Chapman-Enskog method

The transport coefficients of a multi-component hadronic gas at zero and non-zero baryon chemical potential are calculated using the Chapman-Enskog method. The calculations are done within the framework of an $S$-matrix based interacting hadron resonance gas model. In this model, the phase-shifts and cross-sections are calculated using $K$-matrix formalism and where required, by parameterizing the experimental phase-shifts. Using the energy dependence of cross-section, we find the temperature dependence of various transport coefficients such as shear viscosity, bulk viscosity, heat conductivity and diffusion coefficient. We finally compare our results regarding various transport coefficients with previous results in the literature.

Diffractive excitation in pp and pA collisions at high energies

In this paper we consider the Good - Walker approach for the diffractive excitation and updated the Miettinen -- Pumplin (MP) model for $pp/\bar{p}p$ collisions considering the recent LHC data for the total and elastic $pp$ cross sections. The behavior of the total, elastic and diffractive cross sections is analyzed and predictions for the energies of Run 3 of the LHC and those of the Cosmic Rays experiments are derived. Our results demonstrate that the MP model is able to describe the current data and that it implies that the cross section for the diffraction excitation in $pp$ collisions is almost constant in the energy range probed by the LHC and slowly decreases at higher energies. Our results indicate that the Pumplin bound is not reached at the LHC and Cosmic Ray energies. Moreover, the implications of the diffractive excitation in $pA$ collisions is discussed. In particular, the MP model, constrained by the $pp$ data, is used to derive the main quantities present in the treatment of the diffractive excitation in $pA$ collisions. Predictions for the total, elastic and diffractive $pA$ cross sections are presented considering different nuclei. We demonstrate that the effect of fluctuations decreases at larger energies and heavier nuclei. The energy dependence of the diffractive excitation cross section in $pA$ collisions is estimated for different nuclei and compared with the predictions for the proton dissociation induced by photon interactions.

Classical trajectory calculations for state-resolved Penning ionisation reactions of polycyclic aromatic hydrocarbon C10H8 in collision with He*(23S)

ABSTRACTThe reaction dynamics of Penning ionisation of a polycyclic aromatic hydrocarbon (PAH), naphthalene C10H8, in collision with the metastable He*(23S) atom is studied by classical trajectory calculations using an approximate interaction potential energy surface between He* and the molecule, which is constructed based on ab initio calculations for the isovalent Li + C10H8 system. The ionisation width (rate) around the molecular surface are obtained from overlap integrals of the He 1s orbital and the molecular orbital. The calculated collision energy dependences of partial Penning ionisation cross sections (CEDPICS) in the range 50–500 meV at 300 K have reproduced the experimental results semi-quantitatively. The opacity functions, which represent the reaction probability with respect to the impact parameter b, are discussed in connection with collision energy, interaction with He* and the exterior electron density of molecular orbitals. They indicate that the collisional ionisations of C10H8 can be classified into three types: π electron ionisations with negative collision energy dependences which are predominantly determined by attractive interaction with He*; σ orbitals ionisations of the hardcore type; σ orbital ionisations which reflect interaction potentials around CH bonds. The critical impact parameters bc become larger with increasing collision energy due to the centrifugal barrier.

Mechanism and Energetics of the Hydrolysis of Th+ To Form Th(OD)3+: Guided Ion Beam and Theoretical Studies of ThO+, ThO2+, and OThOD+ Reacting with D2O.

The kinetic energy dependences of the reactions of ThO+, ThO2+, and OThOD+ with D2O, ThO2+ with D2, and OThOD+ with Xe were studied using guided ion beam tandem mass spectrometry. Exothermic formation of OThOD+ is the dominant process observed in reactions of both ThO+ and ThO2+ with D2O. Minor products formed in endothermic reactions include ThO2+, DThO+, and ThO2D2+. OThOD+ is also formed in the reaction of ThO2+ with D2 but in an endothermic process. Collision-induced dissociation (CID) of OThOD+ with Xe leads to endothermic loss of the hydroxide ligand. OThOD+ reacts further with D2O to form the associative complex ThO3D3+, which is long-lived before dissociating back to the reactants. The OThOD+-D2O bond energy of the associative complex is measured to be 2.96 ± 0.05 eV by modeling the kinetic energy-dependent cross section for association using a phase space theory model that rigorously conserves angular momentum. By comparison with theory, this bond energy identifies the ThO3D3+ species as the trihydroxide cation, Th(OD)3+. From the endothermic reactions and CID of OThOD+ with Xe, the OTh+-D, OTh+-O, and OTh+-OD bond dissociation energies (BDEs) are measured to be 2.33 ± 0.24, 4.66 ± 0.15, and 6.00 ± 0.17 eV, respectively. All four of these BDEs are experimentally determined for the first time and agree reasonably well with values calculated at the B3LYP, B3PW91, and PBE0 levels of theory with cc-pVQZ basis sets. Complete potential energy surfaces for all reactions were calculated at the B3LYP/cc-pVTZ level and elucidate the mechanisms for all processes observed.

Ion spectroscopy and guided ion beam studies of protonated asparaginyl-threonine decomposition: Influence of a hydroxyl containing C-Terminal residue on deamidation processes

The spontaneous deamidation of asparagine residues plays a significant role in various biological functions and degenerative, aging diseases. Here, we present a full description of the deamidation reaction (as well as other key dissociation processes) of protonated asparaginyl-threonine, [AsnThr + H]+, via complementary infrared multiple photon dissociation (IRMPD) ion spectroscopy, threshold collision-induced dissociation (TCID), and theoretical studies. IRMPD spectra allow for the clear identification of precursor and product ion structural conformations when compared to theoretically calculated spectra for likely structures. Analysis of kinetic energy dependent cross sections measured via TCID with xenon using a guided ion beam tandem mass spectrometer allows for characterization of the energies involved in the decomposition processes of interest. Threshold energies are compared to relative single point energies of major reaction species calculated at B3LYP, B3LYP-GD3BJ, B3P86, and MP2(full) levels of theory, thereby determining important rate-limiting steps involved in [AsnThr + H]+ decomposition. Our studies confirm the formation of a succinimide intermediate via deamidation of [AsnThr + H]+, an observation consistent with condensed-phase deamidation analyses. Interestingly, our spectroscopic results suggest deamidation does not produce furanone isomers even though theoretical results indicate this pathway (exhibited in gas-phase analyses of similar dipeptide systems) should be competitive. Dehydration of [AsnThr + H]+ is also observed, where theory suggests that oxazolone and oxazoline formation are competitive at threshold energies, but IRMPD analyses conclusively confirm the formation of the oxazoline structure. The comprehensive results presented (in addition to complementary studies discussed herein) allow for a valuable analysis of C-terminal residue side-chain effects on the deamidation process.

Bond dissociation energy of Au2 +: A guided ion beam and theoretical investigation.

Guided ion beam tandem mass spectrometry was employed to measure the kinetic energy-dependent product ion cross sections for the collision induced dissociation of Au2 + with Xe. Gold dimer cations were formed in a glow discharge flow tube source that should create ions in their ground electronic state with thermal internal energies. Analysis of the endothermic kinetic energy dependent cross section accounts for multiple collisions, lifetime effects, and the internal energy of the reactant ion. The value obtained for the bond dissociation energy (BDE) of Au2 + is the first direct measurement and is reported here as 2.20 ± 0.21 eV. For comparison with experimental results, theoretical calculations were also completed at the B3LYP, M06-2X, and coupled cluster singles, doubles, and perturbative triples [CCSD(T,full)] levels of theory using the def2-TZVPPD basis set and at the CCSD(T)-F12/correlation-consistent polarized valence triple zeta basis with pseudopotential level. These results predict a 2Σg + electronic ground state for Au2 + with BDEs calculated at the B3LYP and both CCSD(T) levels of theory in agreement with the experiment within the uncertainty. Several electronically excited states are also evaluated theoretically.

Evaluation of the exothermicity of the chemi-ionization reaction Nd + O → NdO+ + e- and neodymium oxide, carbide, dioxide, and carbonyl cation bond energies.

The exothermicity of the chemi-ionization reaction, Nd + O → NdO+ + e-, has been indirectly determined by measuring the thermochemistry for reactions of the lanthanide metal neodymium cation (Nd+) with O2, CO2, and CO and reactions of NdO+ with CO, O2, and Xe. Guided ion beam tandem mass spectrometry was used to measure the kinetic energy dependent product ion cross sections for these reactions. NdO+ is formed through a barrierless exothermic process when the atomic metal cation reacts with O2 and CO2. All other reactions are observed to be endothermic. Analyses of the kinetic energy dependences of these cross sections yield 0 K bond dissociation energies (BDEs) for several species. The 0 K BDE for Nd+-O is determined to be 7.28 ± 0.10 eV from the average of four independent thresholds. This value is combined with the well-established Nd ionization energy to indicate an exothermicity of the title reaction of 1.76 ± 0.10 eV, which is lower and more precise than literature values. In addition, the Nd+-C, ONd+-O, and Nd+-CO BDEs are determined to be 2.61 ± 0.30, 2.12 ± 0.30, and 0.30 ± 0.21 eV. Additionally, theoretical BDEs of Nd+-O, Nd+-C, ONd+-O, and Nd+-CO are calculated at several levels for comparison with the experimental values. B3LYP calculations seriously underestimate the Nd+-O BDE, whereas MP2 and coupled-cluster with single, double-and perturbative triple excitations values are in reasonable agreement. Good agreement is generally obtained for Nd+-C, ONd+-O, and Nd+-CO BDEs as well.

Mass spectrometry of d-ribose molecules

The results of mass spectra of d-ribose molecular beam study by electron impact for the 20–70 eV energy range at the evaporation temperature 310–430 K are presented. The experiment was carried out in two stages: first the mass spectra were measured in the range of 0–200 Da at different ionization energies, then relative cross-sections of single ionization of fragment ions were investigated in the electron energy range of 5–60 eV. The measured temperature dependences show the competing character of water and oxonium cation formation processes. It is the first determination of the appearance energy (AE) for the d-ribose molecule from the threshold region of the energy dependence of the effective ionization cross section. For the most intense fragment ions in the mass spectrum, the potentials of appearance are determined at the threshold of the dissociative ionization cross sections. Schemes for the fragmentation of positive d-ribose ions are proposed.

Thermodynamics and Reaction Mechanisms for Decomposition of a Simple Protonated Tripeptide, H+GAG: a Guided Ion Beam and Computational Study.

We present a thorough characterization of fragmentations observed in threshold collision-induced dissociation (TCID) experiments of protonated glycylalanylglycine (H+GAG) with Xe using a guided ion beam tandem mass spectrometer. Kinetic energy dependent cross sections for nine ionic products were observed and analyzed to provide 0K barriers for the six primary products: [b2]+, [y1 + 2H]+, [b3]+, CO loss, [y2 + 2H]+, and [a1]+; and three secondary products: [a2]+, [a3]+, and CH3CHNH2+, after accounting for multiple ion-molecule collisions, internal energy of reactant ions, unimolecular decay rates, competition between channels, and sequential dissociations. Relaxed potential energy surface scans performed at the B3LYP-GD3BJ/6-311+G(d,p) level of theory are used to identify transition states (TSs) and intermediates of the six primary and one secondary products (where the other two secondary products have mechanisms previously established). Geometry optimizations and single-point energy calculations were performed at several levels of theory. These theoretical energies are compared with experimental threshold energies and are found to give reasonably good agreement, with B3LYP-GD3BJ and M06-2X levels of theory performing better than other levels. The results obtained here are also compared with previous results for decomposition of H+GGG. The primary difference observed is a lowering of the threshold for the [b2]+ product ion and a concomitant suppression of the directly competing [y1 + 2H]+ product, the result of specific methylation of the [b2]+ product ion.

Photoionization of neutral iron from the ground and excited states

The B-spline R-matrix method is used to investigate the photoionization of neutral iron from the ground and excited states in the energy region from the ionization thresholds to 2 Ry. The multiconfiguration Hartree-Fock method in connection with adjustable configuration expansions and term-dependent orbitals is employed for an accurate representation of the initial states of Fe i and the target wave functions of Fe ii. The close-coupling expansion contains 261 LS states of Fe ii and includes all levels of the 3d64s,3d54s2,3d7,3d64p, and 3d54s4p configurations. Full inclusion of all terms from the principal configurations considerably changes both the low-energy resonance structure and the energy dependence of the background cross sections. Partial cross sections are analyzed in detail to clarify the most important scattering channels. Comparison with other calculations is used to place uncertainty bounds on our final photoionization cross sections and to assess the likely uncertainties in the existing data sets.

Photoneutron reaction cross section measurements on Mo94 and Zr90 relevant to the p -process nucleosynthesis

The photodisintegration cross sections for the 94Mo({\gamma},n) and 90Zr({\gamma},n) reactions have been experimentally investigated with quasi-monochromatic photon beams at the High Intensity {\gamma}-ray Source (HI{\gamma}S) facility of the Triangle Universities Nuclear Laboratory (TUNL). The energy dependence of the photoneutron reaction cross sections was measured with high precision from the respective neutron emission thresholds up to 13.5 MeV. These measurements contribute to a broader investigation of nuclear reactions relevant to the understanding of the p-process nucleosynthesis. The results are compared with the predictions of Hauser-Feshbach statistical model calculations using two different models for the dipole {\gamma}-ray strength function. The resulting 94Mo({\gamma},n) and 90Zr({\gamma},n) photoneutron stellar reaction rates as a function of temperature in the typical range of interest for the p-process nucleosynthesis show how sensitive the photoneutron stellar reaction rate can be to the experimental data in the vicinity of the neutron threshold.

Experimental and Computational Study of the Group 1 Metal Cation Chelates with Lysine: Bond Dissociation Energies, Structures, and Structural Trends.

The kinetic energy dependence of the collision-induced dissociation (CID) of Group 1 metal cations (M+ = Li+, Na+, K+, Rb+, and Cs+) chelated to the amino acid lysine (Lys) was measured by threshold CID using a guided ion beam tandem mass spectrometer. The simple loss of neutral lysine is the only dissociation channel observed with the heavier alkali metal cations, whereas CID of Li+(Lys) yields other competing channels including loss of NH3 (the dominant channel at low energy) and eight other reactions. Analysis of the kinetic energy-dependent cross sections yields experimental M+(Lys) bond dissociation energies (BDEs) of 376 ± 30, 219 ± 13, 160 ± 10, 141 ± 6, and 128 ± 4 kJ/mol for Li+, Na+, K+, Rb+, and Cs+, respectively. Computational searches yielded 18 distinct, low-energy structural families related to sites of M+ binding in M+(Lys) complexes and 10 distinct, low-energy structural families for neutral lysine. Among the four levels of theory and three basis sets used, four different ground conformers of M+(Lys) and four different ground conformers of lysine were found, including a ground conformer of K+(Lys) and Cs+(Lys), [Nε,CO(OH)], and its higher energy zwitterionic analogue, [Nε,CO2-], that better explains recent infrared multiple photon dissociation action spectroscopy results. Computational results for predicted ground structures of M+(Lys) complexes yielded computed BDEs in reasonable agreement with experiment.

Features of ω photoproduction off proton target at backward angles: Role of nucleon Reggeon in u -channel with parton contributions

Backward photoproduction of $\omega$ off a proton target is investigated in a Reggeized model where the $u$-channel nucleon Reggeon is constructed from the nucleon Born terms in a gauge invariant way. The $t$-channel meson exchanges are considered as a background. While the $N_\alpha$ trajectory of the nucleon Reggeon reproduces the overall shape of NINA data measured at the Daresbury Laboratory in the range of $u$-channel momentum transfer squared $-1.7<u<0.02$ GeV$^2$ and energies at $E_\gamma=2.8$, 3.5 and 4.7 GeV, a possibility of parton contributions is searched for through the nucleon isoscalar form factor which is parameterized in terms of parton distributions at the $\omega NN$ vertex. Detailed analysis is presented for NINA data to understand the reaction mechanism that could fill up the deep dip from the nucleon Reggeon at momentum squared $u=-0.15$ GeV$^2$. The angle dependence of differential cross sections at the NINA energies above are reproduced in the overall range of $u$ including the CLAS data at forward angles in addition. The energy dependence of the differential cross section is investigated based on the NINA data and the recent LEPS data. A feature of the present approach that implicates parton contributions via nucleon form factor is illustrated in the total and differential cross sections provided by GRAAL and CB-ELSA Collaborations.

PIXE-measurement of Kα X-ray production cross sections for 1-MeV C+-ions in thick samples of Si, Fe, Cu and Zn

Particle-Induced X-ray Emission (PIXE) using heavy ions proved to be an alternative with respect to PIXE using light protons due to relatively large cross sections. In this work we explored the capabilities of PIXE with using singly-charged carbon ions at relatively low energy of 1 MeV (or 83 keV/amu) to measure Kα X-ray production cross sections. The measurement was performed for thick samples of Si, Fe, Cu and Zn, using the standard 2-MeV proton-induced cross sections as the reference. For the measurement from thick samples, we adopted a special multi-slabs method in the calculation by considering the sample thickness effect. The effective ion range was divided into a number of thin slabs in which the energy dependent cross section and the thickness dependent X-ray transmission were varied. The paper describes details of the measurement principle and method and reports the result. The resulting data obtained from the present work were compared with those from the PWBA and ECPSSR theories, the simple thin-film method and the measurement of thin film samples and discussed for the validity of our result.