Energy Transfer Cross Sections Research Articles

Electron Impact Single Ionization Cross Sections of Ar+ Ion

Binary encounter approximation has been used for theoretical calculations of electron impact single ionization cross sections of singly ionized Ar atom at ground state in the energy range of 29.1eV to 2495.1 eV/amu. The cross sections for energy transfer given by Vriens’ and quantum mechanical Hartree-Fock velocity distributions for target electron have been used in the calculation. The contributions in total single ionization cross sections from 3p and 3s subshells are observed higher than from 2p, and the contributions from 3p first increases with impact energy and then decreases with increase of impact energy whereas the contribution from 3s decreases with impact energy. About 69% of results have ratio factors ≤ 1.5 and 59% have values 1.25. Major contributions to the total ionization cross sections are from 3p and 3s for direct single ionization.

Iminothioindoxyl Donors with Exceptionally High Cross Section for Protein Vibrational Energy Transfer.

Various protein functions are related to vibrational energy transfer (VET) as an important mechanism. The underlying transfer pathways can be experimentally followed by ultrafast Vis-pump/IR-probe spectroscopy with a donor-sensor pair of non-canonical amino acids (ncAAs) incorporated in a protein. However, so far only one donor ncAA, azulenylalanine (AzAla), exists, which suffers from a comparably low Vis extinction coefficient. Here, we introduce two novel donor ncAAs based on an iminothioindoxyl (ITI) chromophore. The dimethylamino-ITI (DMA-ITI) and julolidine-ITI (J-ITI) moieties overcome the limitation of AzAla with a 50 times higher Vis extinction coefficient. While ITI moieties are known for ultrafast photoswitching, DMA-ITI and J-ITI exclusively form a hot ground state on the sub-ps timescale instead, which is essential for their usage as vibrational energy donor. In VET measurements of donor-sensor dipeptides we investigate the performance of the new donors. We observe 20 times larger signals compared to the established AzAla donor, which opens unprecedented possibilities for the study of VET in proteins.

Iminothioindoxyl Donors with Exceptionally High Cross Section for Protein Vibrational Energy Transfer

AbstractVarious protein functions are related to vibrational energy transfer (VET) as an important mechanism. The underlying transfer pathways can be experimentally followed by ultrafast Vis‐pump/IR‐probe spectroscopy with a donor‐sensor pair of non‐canonical amino acids (ncAAs) incorporated in a protein. However, so far only one donor ncAA, azulenylalanine (AzAla), exists, which suffers from a comparably low Vis extinction coefficient. Here, we introduce two novel donor ncAAs based on an iminothioindoxyl (ITI) chromophore. The dimethylamino‐ITI (DMA‐ITI) and julolidine‐ITI (J‐ITI) moieties overcome the limitation of AzAla with a 50 times higher Vis extinction coefficient. While ITI moieties are known for ultrafast photoswitching, DMA‐ITI and J‐ITI exclusively form a hot ground state on the sub‐ps timescale instead, which is essential for their usage as vibrational energy donor. In VET measurements of donor‐sensor dipeptides we investigate the performance of the new donors. We observe 20 times larger signals compared to the established AzAla donor, which opens unprecedented possibilities for the study of VET in proteins.

Differential Cross Sections for Pair-Correlated Rotational Energy Transfer in NO(A2Σ+) + N2, CO, and O2: Signatures of Quenching Dynamics.

A crossed molecular beam, velocity-map ion-imaging apparatus has been used to determine differential cross sections (DCSs), as a function of collider final internal energy, for rotationally inelastic scattering of NO(A2Σ+, v = 0, j = 0.5f1) with N2, CO, and O2, at average collision energies close to 800 cm-1. DCSs are strongly forward scattered for all three colliders for all observed NO(A) final rotational states, N'. For collisions with N2 and CO, the fraction of NO(A) that is scattered sideways and backward increases with increasing N', as does the internal rotational excitation of the colliders, with N2 having the highest internal excitation. In contrast, the DCSs for collisions with O2 are essentially only forward scattered, with little rotational excitation of the O2. The sideways and backward scattering expected from low-impact-parameter collisions, and the rotational excitation expected from the orientational dependence of published van der Waals potential energy surfaces (PESs), are absent in the observed NO(A) + O2 results. This is consistent with the removal of these short-range scattering trajectories via facile electronic quenching of NO(A) by O2, in agreement with the literature determination of the coupled NO-O2 PESs and the associated conical intersections. In contrast, collisions at high-impact parameter that predominately sample the attractive van der Waals minimum do not experience quenching and are inelastically forward scattered with low rotational excitation.

Neutrino Spectra of Magneto-Rotational Supernovae and Observations Using Large-Volume Telescopes

The dynamics of neutrinos in hot and dense magnetized matter, corresponding to a magneto-rotational explosion of supernovae, is considered. It is shown that the effective collisions of neutrinos in a magnetized nucleon gas, due to the Gamow–Teller component of the neutral current, change from exo- to endo-energetic scattering, when the neutrino energy becomes approximately four times higher than the temperature of the substance. Correspondingly, the energy transfer cross section in the neutrino kinetics changes from positive to negative values under these conditions. For realistic parameters of supernovae, the considered effects lead to an increase in the hardness of the neutrino spectra. The possibilities of detecting supernova neutrinos by large-volume observatories KM3NeT and Baikal-GVD are discussed.

Radiation shielding characterization of 83Bi209, 74W184, 50Sn119, ZnS, and CaCO3 using the modified Klein-Nishina formula

Radiation has many beneficial applications, particularly in healthcare and medicine. However, due to its hazards and adverse effects on human health, it is important to investigate materials for radiation shielding and protection purposes. In the present work, the electronic cross-sections, atomic cross-section, transfer cross-sections, Compton mass attenuation coefficients, and mass-energy transfer coefficients of 83Bi209, 74W184, 50Sn119, ZnS, and CaCO3 have been investigated using γ-ray energies ranging from 0.5 MeV to 18 MeV, by application of the Klein-Nishina formula. The results show that the electronic, atomic, and energy transfer cross-sections decrease with increasing γ-ray energy. The mass attenuation coefficients were observed to increase as the Z/A ratio increased. The mass energy-transfer coefficients decreased with an increasing Z/A ratio The Z/A ratio is an essential characteristic of a shielding material because it affects the scatter and absorption of γ-ray energy after a collision with an atom. The materials are found to be very suitable for radiation shielding and protection purpose. The investigated elements and compounds can also be used as lead alternative materials, to avoid environmental toxicity.

Optimization and inference of bin widths for histogramming inelastic neutron scattering spectra.

A data-driven bin-width optimization for the histograms of measured data sets based on inhomogeneous Poisson processes was developed in a neurophysiology study [Shimazaki & Shinomoto (2007). Neural Comput. 19, 1503-1527], and a subsequent study [Muto, Sakamoto, Matsuura, Arima & Okada (2019). J. Phys. Soc. Jpn, 88, 044002] proposed its application to inelastic neutron scattering (INS) data. In the present study, the results of the method on experimental INS time-of-flight data collected under different measurement conditions from a copper single crystal are validated. The extrapolation of the statistics on a given data set to other data sets with different total counts precisely infers the optimal bin widths on the latter. The histograms with the optimized bin widths statistically verify two fine-spectral-feature examples in the energy and momentum transfer cross sections: (i) the existence of phonon band gaps; and (ii) the number of plural phonon branches located close to each other. This indicates that the applied method helps in the efficient and rigorous observation of spectral structures important in physics and materials science like novel forms of magnetic excitation and phonon states correlated to thermal conductivities.

Differential Condensation of Methane Isotopologues Leading to Isotopic Enrichment under Non-equilibrium Gas-Surface Collision Conditions.

We examine the initial differential sticking probability of CH4 and CD4 on CH4 and CD4 ices under nonequilibrium flow conditions using a combination of experimental methods and numerical simulations. The experimental methods include time-resolved in situ reflection–absorption infrared spectroscopy (RAIRS) for monitoring on-surface gaseous condensation and complementary King and Wells mass spectrometry techniques for monitoring sticking probabilities that provide confirmatory results via a second independent measurement method. Seeded supersonic beams are employed so that the entrained CH4 and CD4 have the same incident velocity but different kinetic energies and momenta. We found that as the incident velocity of CH4 and CD4 increases, the sticking probabilities for both molecules on a CH4 condensed film decrease systematically, but that preferential sticking and condensation occur for CD4. These observations differ when condensed CD4 is used as the target interface, indicating that the film’s phonon and rovibrational densities of states, and collisional energy transfer cross sections, have a role in differential energy accommodation between isotopically substituted incident species. Lastly, we employed a mixed incident supersonic beam composed of both CH4 and CD4 in a 3:1 ratio and measured the condensate composition as well as the sticking probability. When doing so, we see the same effect in the condensed mixed film, supporting an isotopic enrichment of the heavier isotope. We propose that enhanced multi-phonon interactions and inelastic cross sections between the incident CD4 projectile and the CH4 film allow for more efficacious gas–surface energy transfer. VENUS code MD simulations show the same sticking probability differences between isotopologues as observed in the gas–surface scattering experiments. Ongoing analyses of these trajectories will provide additional insights into energy and momentum transfer between the incident species and the interface. These results offer a new route for isotope enrichment via preferential condensation of heavier isotopes and isotopologues during gas–surface collisions under specifically selected substrate, gas-mixture, and incident velocity conditions. They also yield valuable insights into gaseous condensation under non-equilibrium conditions such as occur in aircraft flight in low-temperature environments. Moreover, these results can help to explain the increased abundance of deuterium in solar system planets and can be incorporated into astrophysical models of interstellar icy dust grain surface processes.

He2+ Impact Single Ionization Cross Sections of Fe Atom

Binary encounter approximation has been used for theoretical calculations of alpha particle (He2+) impact single ionization cross sections of iron atom at ground state in the energy range of 35 to 360 keV/amu. The cross sections for energy transfer given by Vriens’ and quantum mechanical Hartree-Fock velocity distributions for target electron have been used in the calculation. The contributions in total single ionization cross sections from 4s and 3d subshells are observed to be higher than from 3p, and the contributions from 4s decreases with increase of impact energy whereas the contribution from 3d increases. The total single ionization cross sections decrease gradually with the increase of impact energy similar to experimental results which implies that our results are in satisfactory agreement with the experimental data in the given energy range.

Impact of Complex Logic Cell Layout on the Single-Event Transient Sensitivity

The design methodology based on standard cells is widely used in a broad range of very-large-scale integration (VLSI) applications. Furthermore, several optimization algorithms can be employed to address different constraints such as power consumption or reliability. This paper evaluates the implications of the usage of complex logic cells from a 45-nm standard-cell library to the single-event transient (SET) sensitivity under heavy ions. Results show that even though a reduction in the layout area is obtained when adopting complex logic gates, a slight reduction in the total sensitive area of the circuit is observed. Moreover, the effectiveness of the logical masking can be suppressed, leading to a higher SET cross section for high particle linear energy transfer (LET).

Determination of the energy transfer section between CdS semiconductor quantum dots and Nd3+ ions

This paper proposes, for the first time, a quantitative description of the cross section of energy transfer between Nd3+ ions and quantum dots through rate equations model. Nd3+ ions were embedded in a SNAB glass system with CdS quantum dots. This occurred because the Nd3+ ions absorbed photons emitted by CdS quantum dots with 457 nm excitation. Band overlap of the quantum dots luminescence band with the ion optical absorption bands caused photon absorption and produced valleys in the quantum dots luminescence spectrum. The energy transfer occurred via photon. The cross section of energy transfer was higher than that found in other semiconductor systems with rare earth.

A full-dimensional potential energy surface and quantum dynamics of inelastic collision process for H2-HF.

A full-dimensional ab initio potential energy surface for the H2-HF van der Waals complex was constructed by employing the coupled-cluster singles and doubles with noniterative inclusion of connected triples with augmented correlation-consistent polarised valence quadruple-zeta basis set plus bond functions. Using the improved coupled-states approximation including the nearest neighbor Coriolis couplings, we calculated the state-to-state scattering dynamics for pure rotational and ro-vibrational energy transfer processes. For pure rotational energy transfer, our results showed a different dynamical behavior for para-H2 and ortho-H2 in collision with hydrogen fluoride (HF), which is consistent with the previous study. Interestingly, some strong resonant peaks were presented in the cross sections for ro-vibrational energy transfer. In addition, the calculated vibrational-resolved rate constant is in agreement with the experimental results reported by Bott et al. These dynamics data can be further applied to the numerical simulation of HF chemical lasers.

Klein–Nishina electronic cross-section, Compton cross sections, and buildup factor of wax for radiation shielding and protection

Klein–Nishina scattering cross-sections, Compton scattering, mass attenuation and energy transfer cross-sections, linear attenuation coefficient and buildup factor of 99.99% pure paraffin wax (Carbon = 85.14%, Hydrogen = 14.86%). are calculated using 0.662, 0.835, 1.17 and 1.33 MeV γ-rays. The mentioned γ-rays were obtained from Cs-137, Mn-54 and Co-60 radioisotopes. Gamma rays obtained from these radioisotopes were passed through circular shaped wax slices and allowed to fall on a NaI detector. The thickness of wax slices were 0.33–2.9 cm with 6 cm diameter. Lead collimator of 1 cm diameter hole in the middle was used to obtain a collimated beam for narrow beam geometry. Broad beam geometry was used by removing the collimator to investigate buildup factor. Results show that Klein–Nishina electronic cross-section, Compton mass attenuation coefficient and Compton energy transfer coefficient all decrease with increasing photon energy. Linear attenuation coefficients μ = 0.0532 cm−1 for 1.17 MeV beam and μ = 0.0419 cm−1 for 1.33 MeV γ-rays were obtained for wax. Variations in buildup factors are observed with increasing thickness of wax for 1.17 and 1.33 MeV beams.

Ian William Murison Smith. 15 June 1937—8 November 2016

Ian Smith was one of the world-wide leading researchers into reaction kinetics, energy transfer and molecular dynamics in gas phase systems. He was able to span all of these aspects of collisional behaviour, and to form connections and insights that allowed him to make advances in all of them, advances which have stood the tests of time. His graduate work at the University of Cambridge was followed by academic positions in Cambridge and in Birmingham. He provided new insights into molecular energy transfer by systematically measuring how vibrational frequencies and multipole moments influenced the magnitude of the energy transfer cross sections. In reaction kinetics his detailed work on the OH radical has led to an understanding of the importance of its reactions not only in applied areas such as atmospheric and combustion chemistry, but also in fundamental dynamical studies of radical recombination and the effect of reagent energies on reactive processes. Of particular significance has been his development of both cryogenic and nozzle expansion methods of studying collisional processes at temperatures down to 10 K, with the discovery that reactions without activation barriers can get faster as the temperature decreases. The impact of this work upon astrochemistry has been profound, and has stimulated theoretical explanations of the effect. He was one of the first pioneers in the UK of the use of laser techniques to study collisional processes, using laser-induced fluorescence as a sensitive detection tool, UV laser photolysis to form reactive species and laser pumping to create excited state populations in order to observe their effect upon reaction pathways and vibrational relaxation. Ian was devoted to his family—his wife Sue, their four children and 11 grandchildren. His research collaborators will always remember his scholarship, his unending suggestions of interesting problems to study, his deep integrity and humanity. His legacy lives on with his personal and academic families.

Control of the luminescent properties of Eu2-xDyx(WO4)3 solid solutions for scintillator applications

Crystalline materials containing tungsten and europium ions are frequently used as scintillators because tungsten complexes show a high absorption cross section for high energy radiation and efficient energy transfer to europium ions, which relax radiatively in the visible spectral range according to the 5D0→7F2 transition. However, this intra-configurational transition is forbidden on spin and parity and, consequently, shows a slow decay rate (hundreds of microseconds to milliseconds). In order to use this kind of materials in high repetition rate processes, faster luminescence decays are required. A set of Eu2-xDyx(WO4)3 solid solutions has been synthesized. Rietveld refinement of X-ray diffraction patterns has been performed in order to determine the crystalline structure of the samples and particularly the distance between rare earth cations. The morphology and composition was characterized with scanning electron microscopy combined with energy-dispersive X-ray spectroscopy. Optical absorption, emission spectra and decay rates have been systematically measured to analyze the luminescent properties of the materials. Cross-relaxation processes between Eu3+ and Dy3+ ions are responsible of the reduction of the 5D0 decay rate. The average lifetime of the Eu3+5D0 excited state can be decreased in the range of one order of magnitude. However, the 5D0→7F2 emission intensity decreases in the same range too. Nevertheless, the proposed strategy of Eu3+5D0 lifetime reduction can be of interest for those opto-electronic detection applications, which are not limited by sensitivity but by time resolution, such as it occurs in many cases for high energy-high repetition rate photon pulses.

Rotational energy transfer in collisions between CO and Ar at temperatures from 293 to 30 K

Experimental measurements and theoretical calculations are reported for rotational energy transfer in the Ar-CO system. Experiments were performed in cold uniform supersonic flows of Ar, using an infrared – vacuum ultraviolet double resonance technique to measure absolute state-to-state rate constants and total relaxation cross sections for rotational energy transfer within the (v=2) vibrational state of CO in collision with Ar at temperatures from 30.5 to 293K. Close-coupling calculations were also performed using a recent potential energy surface (Sumiyoshi and Endo, 2015). Very good agreement is obtained between measured and calculated values.

Nondestructive detection of polar molecules via Rydberg atoms

A highly sensitive, general, and preferably nondestructive technique to detect polar molecules would greatly advance a number of fields, in particular quantum science with cold and ultracold molecules. Here, we propose using resonant energy transfer between molecules and Rydberg atoms to detect molecules. Based on an energy transfer cross-section of > 10−6 cm2 for sufficiently low collision energies, a near unit efficiency non-destructive detection of basically any polar molecule species in a well-defined internal state should be possible.

Large cross section for super energy transfer from hyperthermal atoms to ambient molecules

The experimentally measured cross section for super energy transfer collisions between a hyperthermal H atom and an ambient molecule is presented here. This measurement substantiates an emerging energy transfer mechanism with significant cross section, whereby a major fraction of atomic translational energy is converted into molecular vibrational energy through a transient collision-induced reactive complex. Specifically, using nanosecond time-resolved infrared emission spectroscopy, it is revealed that collisions between hyperthermal hydrogen atoms (with 59 kcal/mol of kinetic energy) and ambient ${\mathrm{SO}}_{2}$ result in the production of vibrationally highly excited ${\mathrm{SO}}_{2}$ with $g14\phantom{\rule{0.16em}{0ex}}000\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ of internal energy. The lower limit of the cross section for this super energy transfer process is determined to be $0.53\ifmmode\pm\else\textpm\fi{}0.05$ \AA{}${}^{2}$, i.e., 2% of all hard-sphere collisions. This cross section is orders of magnitude greater than that predicted by the exponential energy gap law, which is commonly used for describing collisional energy transfer through repulsive interactions.

Parity-Dependent Rotational Energy Transfer in CN(A2Π, ν = 4, j F1ε) + N2, O2, and CO2 Collisions

We report state-resolved total removal cross sections and state-to-state rotational energy transfer (RET) cross sections for collisions of CN(A2Π, ν = 4, jF1ε) with N2, O2, and CO2. CN(X2Σ+) was produced by 266 nm photolysis of ICN in a thermal bath (296 K) of the collider gas. A circularly polarized pulse from a dye laser prepared CN(A2Π, ν = 4) in a range of F1e rotational states, j = 2.5, 3.5, 6.5, 11.5, 13.5, and 18.5. These prepared states were monitored using the circularly polarized output of an external cavity diode laser by frequency-modulated (FM) spectroscopy on the CN(A–X)(4,2) band. The FM Doppler profiles were analyzed as a function of pump–probe delay to determine the time dependence of the population of the initially prepared states. Kinetic analysis of the resulting time dependences was used to determine total removal cross sections from the initially prepared levels. In addition, a range of j′ F1e and j′ F2f product states resulting from rotational energy transfer out of the j = 6.5 F1e initial state were probed, from which state-to-state RET cross sections were measured. The total removal cross sections lie in the order CO2 > N2 > O2, with evidence for substantial cross sections for electronic and/or reactive quenching of CN(A, ν = 4) to unobserved products with CO2 and O2. This is supported by the magnitude of the state-to-state RET cross sections, where a deficit of transferred population is apparent for CO2 and O2. A strong propensity for conservation of rotational parity in RET is observed for all three colliders. Spin–orbit-changing cross sections are approximately half of those of the respective conserving cross sections. These results are in marked disagreement with previous experimental observations with N2 as a collider but are in good agreement with quantum scattering calculations from the same study (Khachatrian et al. J. Phys. Chem. A2009, 113, 392219215110). Our results with CO2 as a collider are similarly in strong disagreement with a related experimental study (Khachatrian et al. J. Phys. Chem. A2009, 113, 1339019405498). We therefore propose that the previous experiments substantially underestimated the spin–orbit-changing cross sections for collisions with both N2 and CO2, suggesting that even approximate quantum scattering calculations may be more successful for such molecule–molecule systems than was previously concluded.

A MOLECULAR DYNAMICS STUDY ON SLOW ION INTERACTIONS WITH THE POLYCYCLIC AROMATIC HYDROCARBON MOLECULE ANTHRACENE

Atomic collisions with polycyclic aromatic hydrocarbon (PAH) molecules are astrophysically particularly relevant for collision energies of less than 1 keV. In this regime, the interaction dynamics are dominated by elastic interactions. We have employed a molecular dynamics simulation based on analytical interaction potentials to model the interaction of low energy hydrogen and helium projectiles with isolated anthracene (C14H10) molecules. This approach allows for a very detailed investigation of the elastic interaction dynamics on an event by event basis. From the simulation data the threshold projectile kinetic energies above which direct C atom knock out sets in were determined. Anthracene differential energy transfer cross sections and total (dissociation) cross sections were computed for a wide range of projectile kinetic energies. The obtained results are interpreted in the context of PAH destruction in astrophysical environments.