High Ionization Potential Research Articles

The theoretical investigation of the opto-electronic properties of designed molecules having 2-(2-Methylene-3-oxo-indane-1-ylidene)malononitrile as end-capped acceptors

Abstract Five acceptor-donor-acceptor molecules having different core units with 2-(2-Methylene-3-oxo-indane-1-ylidene)malononitrile as end capped terminal acceptor unit were designed. The ground state geometries and electronic properties were calculated by using density functional theory (DFT) at MPW1PW91/6-31G(d,p) level of theory. The absorption spectra were computed by using time dependent DFT at MPW1PW91/6-31G(d,p) level of theory. The designed molecules have broad absorption range in visible region. M3 shows relatively lower band gap so that having high light harvesting efficiency (LHE). The molecules consider as better hole blocking materials in term of high ionization potentials. The reorganization energies calculation of M1, M2 and M4 manifests that these molecules are the optimal candidate for electron transportation. High value of Voc has been observed for molecules which would favorably contribute in power conversion efficiency. M1, M2, M4 and M5 are more stable in terms of absolute hardness and electrostatic potential surfaces. All molecules show good opto-electronic properties in the aspect of their use in photovoltaic application.

The theoretical investigation of the opto-electronic properties of designed molecules having 2-(2-Methylene-3-oxo-indane-1-ylidene)malononitrile as end-capped acceptors

Abstract Five acceptor-donor-acceptor molecules having different core units with 2-(2-Methylene-3-oxo-indane-1-ylidene)malononitrile as end capped terminal acceptor unit were designed. The ground state geometries and electronic properties were calculated by using density functional theory (DFT) at MPW1PW91/6-31G(d,p) level of theory. The absorption spectra were computed by using time dependent DFT at MPW1PW91/6-31G(d,p) level of theory. The designed molecules have broad absorption range in visible region. M3 shows relatively lower band gap so that having high light harvesting efficiency (LHE). The molecules consider as better hole blocking materials in term of high ionization potentials. The reorganization energies calculation of M1, M2 and M4 manifests that these molecules are the optimal candidate for electron transportation. High value of Voc has been observed for molecules which would favorably contribute in power conversion efficiency. M1, M2, M4 and M5 are more stable in terms of absolute hardness and electrostatic potential surfaces. All molecules show good opto-electronic properties in the aspect of their use in photovoltaic application.

Nonsequential double ionization of alkaline-earth metal atoms by intense mid-infrared femtosecond pulses.

A systematic study of nonsequential double ionization (NSDI) of alkaline-earth metal atoms with mid-infrared femtosecond pulses is reported. We find that the measured NSDI yield shows a strong target dependence and it is more suppressed for alkaline-earth metal with higher ionization potential. The observation is attributed to the differences in the recollision induced excitation and ionization cross sections of alkaline-earth metals. This work indicates that NSDI of alkaline-earth metals can be generally understood within recollision picture and sheds light on ultrafast control of electron correlation and dynamics of ionic excited states during NSDI of atoms with complex structures.

Onthe changes in the physical properties of the ionized region around the Weigelt structures in η Carinae over the 5.54-yr spectroscopic cycle

ABSTRACT We present HST/STIS observations and analysis of two prominent nebular structures around the central source of η Carinae, the knots C and D. The former is brighter than the latter for emission lines from intermediate- or high-ionization potential ions. The brightness of lines from intermediate- and high-ionization potential ions significantly decreases at phases around periastron. We do not see conspicuous changes in the brightness of lines from low-ionization potential (<13.6 eV) ions over the orbital period. Line ratios suggest that the total extinction towards the Weigelt structures is AV = 2.0. Weigelt C and D are characterized by an electron density of 106.9 cm−3 that does not significantly change throughout the orbital cycle. The electron temperature varies from 5500 (around periastron) to 7200 K (around apastron). The relative changes in the brightness of the He i lines are well reproduced by the variations in the electron temperature alone. We found that, at phases around periastron, the electron temperature seems to be higher for Weigelt C than that of D. The Weigelt structures are located close to the Homunculus equatorial plane, at a distance of about 1240 au from the central source. From the analysis of proper motion and age, the Weigelt complex can be associated with the equatorial structure called ‘Butterfly Nebula’ surrounding the central binary system.

Improvement of ionization yield in sputtered neutral mass spectrometry using pulsed infrared and ultraviolet lasers

A new laser ionization method for sputtered neutral mass spectrometry (SNMS), which the authors call “dual-laser SNMS,” was developed to increase the ionization probability and improve sensitivity. In this technique, pulsed IR and UV lasers irradiated sputtered atoms simultaneously, while the additional UV laser pulse enhanced the ionization process. The useful yields of the target elements increased by 10%–20% compared to using the IR irradiation alone, and the yield increased with increasing UV power. In addition, there was little correlation between the ionization potential and the ratio of the ionization enhancement. Therefore, dual-laser SNMS was effective for the analysis of elements with higher ionization potential.

Refined composition of Solar Wind xenon delivered by Genesis NASA mission: Comparison with xenon captured by extraterrestrial regolith soils

The Genesis mission captured Solar Wind (SW) and delivered it to Earth for laboratory analyses. Due to advanced mass spectrometric techniques developed specifically for analyses of returned Genesis SW-collectors, SW-oxygen, nitrogen and noble gas isotopes have been successfully measured providing new insights for cosmo- and geochemistry. SW-Xe collected by Genesis is the heaviest and the least abundant SW element analyzed. Here we describe in detail the experimental improvements we made over last 5 years and a latest refined SW-Xe isotopic composition. Combined with earlier, already published SW-Xe analyses, our new results provide the best current estimate for SW-Xe collected by Genesis: 136Xe/130Xe = 1.818 ± 0.004; 134Xe/130Xe = 2.242 ± 0.005; 132Xe/130Xe = 6.063 ± 0.010; 131Xe/130Xe = 5.010 ± 0.012; 129Xe/130Xe = 6.314 ± 0.013; 128Xe/130Xe = 0.510 ± 0.001; 126Xe/130Xe = 0.0256 ± 0.0004; 124Xe/130Xe = 0.0292 ± 0.0004 (all errors are 1σ). The achieved precision allows resolving small, but now statistically significant isotopic difference between solar wind Xe and Xe trapped in lunar regolith samples. This emerging difference, not apparent prior to this study, likely points to the composition of indigenous lunar Xe and to the temporal evolution of terrestrial Xe.Combining our Xe fluence with that for other high first ionization potential (FIP) elements, we find that the depletion of elements with the FIP greater than 12 eV is not constant but monotonically decreases as FIP increases.

HST/COS Observations of Quasar Outflows in the 500–1050 Å Rest Frame. V. Richness of Physical Diagnostics and Ionization Potential-dependent Velocity Shift in PKS J0352-0711*

Abstract We analyze absorption troughs from two outflows within PKS J0352-0711 (S1 at −1950 km s−1 and S2 at −3150 km s−1) from spectra taken with Hubble Space Telescope/Cosmic Origins Spectrograph, which cover the diagnostic-rich 585–900 Å rest-frame wavelength range. In S2, for the first time we clearly detect absorption troughs from Ca iv, Ca v, Ca v*, Ca vii*, and Ca viii*. The column density measurement of Ca v suggests S2 has a super-solar metallicity. Both outflows require at least two ionization phases where the column density of the very high-ionization phase is roughly 15 times larger than the corresponding high-ionization phase. These high column densities and very high-ionization potential ions are similar to X-ray warm absorbers. The two phases of S2 show a unique velocity centroid shift between associated troughs. Through Monte Carlo measurements of the O v* absorption troughs, we determine the electron number density of S2 (fully corroborated by independent measurements from the Ca vii* and Ca viii* troughs), yielding a distance of 9 pc and a kinetic luminosity of 2 × 1043 erg s−1. S1 is located farther away at 500 pc from the central source with a kinetic luminosity of 1043 erg s−1.

Dipolar hole-blocking layers for inverted perovskite solar cells: effects of aggregation and electron transport levels

Herein, we report on the synthesis and investigation of two triazino-isoquinoline tetrafluoroborate electrolytes as hole-blocking layers in methylammonium triiodide perovskite photovoltaic devices with fullerene electron extraction layer. We find that increasing the thickness of the dipolar hole-blocking layer results in a gradual increase in the open-circuit voltage suggesting that aggregation of the molecules can enhance the dipole induced by the layer. This finding is confirmed by theoretical calculations demonstrating that while both molecules exhibit a similar dipole moment in their isolated state, this dipole is significantly enhanced when they aggregate. Ultra-violet photoemission spectroscopy measurements show that both derivatives exhibit a high ionization potential of 7 eV, in agreement with their effective hole-blocking nature demonstrated by the devices. However, each of the molecules shows a different electron affinity due to the increased conjugation of one of the derivatives. While the change in electron transport level between the two derivatives is as high as 0.3 eV, the difference in the open-circuit voltage of both types of devices is negligible, suggesting that the electron transport level plays only a minor role in determining the open-circuit voltage of the device. Numerical device simulations confirm that the increase in built-in potential, arising from the high dipole of the electrolyte layer, compensates for the non-ideal energetic alignment of the charge transport levels, resulting in high open-circuit voltages for a range of electron transport levels. Our study demonstrates that the application of small molecule electrolytes as hole-blocking layer in inverted architecture perovskite solar cells is a powerful tool to enhance the open-circuit voltage and provides useful guidelines for designing future generations of such compounds.

Emittance preservation through density ramp matching sections in a plasma wakefield accelerator

In plasma wakefield acceleration, the witness beam's emittance needs to be preserved when it propagates through a plasma stage. The plasma includes density ramps at both the entrance and the exit. Using the Wentzel-Kramers-Brillouin solution of a single particle's motion, analytical expressions for the evolution of the beam emittance and the Twiss parameters in an arbitrary adiabatic plasma profile are provided neglecting the acceleration of the beam inside the plasma. It is shown that the beam emittance can be preserved under the matching condition even when the beam has an initial energy spread. It is also shown that the emittance growth for an unmatched beam is minimized when it is focused to the same vacuum plane for a matched beam. The emittance evolution from 3D QuickPIC simulation results agree well with the theoretical results. In the some of the proposed experiments on nearly completed FACET II facility, the matching condition may not be perfectly satisfied and the wake may not be perfectly symmetric. It is shown that for a given set of beam parameters that are consistent with FACET II capabilities, even when the assumptions of the theory are not satisfied, the emittance growth can still be minimized by choosing the optimal focal plane. Last, another issue that may cause emittance growth in realistic plasmas is also examined. When using a lithium plasma source in FACET II experiments a helium buffer gas is used. The plasma is formed from field ionization which can lead to a nonlinear focusing force when there are nonuniform helium ions due to its high ionization potential. For an initial beam emittance of $20\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$, the helium ionization is found to be small and the witness beam's emittance can be preserved.

A Highly Sensitive Zirconium Hydrogen Phosphate Emitter for Ni Isotope Determination Using Thermal Ionization Mass Spectrometry

The nickel isotope has a great potential for investigating biogeochemical processes in the geosciences and has been proven to be extremely useful for studying the chronology of the early solar system. As one of the most powerful techniques in metal isotopic ratio measurements, thermal ionization mass spectrometry (TIMS) shows poor sensitivity for Ni isotope ratio analysis, because the high ionization potential (7.640eV) of Ni makes it difficult to be ionized on a hot filament. In previous studies, a minimum of 1000 ng Ni was required using the classical Sigel-H3BO3-Al emitter or the Sigel-H3PO4-Al emitter. The present study is first to employ a highly sensitive zirconium hydrogen phosphate (Zr(HPO4)2) emitter to measure the Ni isotopes with TIMS. This emitter produces a significant enhancement in the ionization efficiency of Ni and enables the analysis of the Ni isotope at the 200 ng level with high precision. In addition, this newly developed emitter shows a strong inhibition to the Fe and Zn signals, which are the main potential isobaric interferences during Ni measurement. A series of analyses of the NIST SRM 986 standard demonstrated that an internal precision (2 RSE) of ± 0.03 to 0.05 ‰ can be achieved depending on the sample size. Analysis of the NIST SRM 986 standard also shows an external reproducibility (2 RSD, n = 10) of better than ± 0.11‰, even for Ni at 200 ng.

Determining the Physical Parameters of the System V1413 Aql in Its Quiescent and Active States in 20122017

We present the results of our spectroscopic observations for the classical symbiotic star V1413 Aql in 20122017. In this period the system was in both active and rare (for it) quiescent states. In 2012 the optical spectrum was dominated by the radiation from the erupted hot component of spectral type F47 III. In 2017 the system passed to a quiescent state that lasted at least three months. In this period lines of ions with high ionization potentials, such as He II 4686 A and CIV 5802 A, appeared in the spectrum. The temperature and luminosity of the hot component in this period were $$T_{\textrm{hot}}\approx 90\,000$$ K and $$L_{\textrm{hot}}\approx 1800L_{\odot}$$. We show that the quiescent state in 2017 differs little in its time and energy characteristics from the previous active state observed in 1993.

氧气对飞秒激光泵浦的氮气分子无腔激光效应的淬灭作用（特邀）

Nitrogen gas pumped by circularly polarized femtosecond laser pulses gives rise to bidirectional lasing emission，which holds unique potential for remote optical sensing application. However，the presence of oxygen molecules strongly suppresses this lasing effect. The influence of O2，Kr，Ar and He on the lasing effect of nitrogen molecules was compared，and the fluorescence of nitrogen molecules in pure nitrogen and ambient air was examined. It is observed that the lasing presents a similar quenching effect with the partial pressure of O2 and Kr，since Kr has a close ionization potential compared to O2. In contrast， for He which has a much higher ionization potential，there is no significant quenching effect. Therefore it is suggested that the quenching effect of O2 on nitrogen molecules mainly stems from the fact that O2 leads to a reduction of the clamped laser intensity inside the plasma filaments，which results in a decrease of the kinetic energy of the free electrons and an inefficient collision excitation.

Metastability triggered reactivity in clusters at realistic conditions: a case study of N-doped (TiO2) n for photocatalysis

We present a strategy, by taking a prototypical model system for photocatalysis (viz. N-doped (TiO2) n clusters), to accurately design photocatalyst with enhanced reactivity at a given environmental conditions (i.e. temperature (T), pressure () and doping (µ e )). Since free energy potential energy surface consists of many competing isomers even in a small energy window, computational design of specific metastable photocatalysts with enhanced activity is extremely challenging. This requires fixing various parameters as follows; (i) favorable formation energy, (ii) low fundamental gap, (iii) low excitation energy, (iv) high vertical electron affinity (VEA) and (v) low vertical ionization potential (VIP) to drive the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) for water splitting. Here, we show that by integrating several first principles based methodologies that consideration of the global minimum structure alone can severely underestimate the activity. First, we have used a suite of genetic algorithms (namely, searching clusters with conventional minimum total energy ((GA)); searching clusters with specific property i.e. high VEA ((GA)), and low VIP ((GA))) to model the N-doped (TiO2) n ( n = 4–10, 15, 20) (meta)stable clusters. Next, we have identified its free energy using ab initio atomistic thermodynamics to confirm that the metastable structures are not too far from the free energy global minima. We find that N-substitution ((N)) prefers to reside at highly coordinated oxygen site, whereas N-interstitial ((NO)) and split-interstitial ((N) favor the dangling oxygen site. (NO) and (N doped states are thermodynamically stable at finite temperature (T) and pressure (). Interestingly, each types of defect (viz. substitution, interstitials) reduce the fundamental gap and excitation energy substantially. However, (N doped clusters are found to be less probable in the Pourbaix phase diagram, whereas (N) and (NO) doped metastable clusters show significant occupance probability near the phase boundaries. The latter ensures much higher electrocatalytic activity for water splitting than the most stable configurations.

A correlation-relaxation-balanced direct method at the second order perturbation theory for accurate ionization potential predictions.

The development of a quasi-particle approach for an accurate yet efficient prediction of a complete ionization potential (IP) spectrum, from valence down to core electrons for the system of interest, is a long-cherished goal in quantum chemistry. Based on the physical understanding of the electron correlation and relaxation effects at the second order perturbation theory, we present here a correlation-relaxation-balanced direct method, dubbed CRB-MP2, via a parameter scaled scheme of the 2ph (two-particle, one-hole summation) and 2hp (two-hole, one-particle summation) terms. With almost no extra computational cost after a normal MP2 procedure, the CRB-MP2 method yields high quality valence and core IPs for a wide range of species. A direct approach for complete IP spectrum calculations with both computational accuracy and efficiency is therefore established.

Structural and Electronic Properties of Binary Clusters SimGen (m + n = 6–13)

Using genetic algorithm combined with density functional theory calculations, we performed an unbiased global search for the most-stable structures of binary clusters SimGen with size s = m + n from 6 to 13. Further, we studied the structural and electronic properties of SimGen clusters using the B3LYP and CCSD(T) methods coupled with 6-311G + (d) basis set. For s = 6-12, SimGes-m clusters exhibit similar geometries to Sis and Ges clusters, respectively. However, for s = 13, the geometries of SimGes-m clusters fall into five completely different patterns. The negative mixing energies of SimGes-m clusters indicate that they possess higher energetic stability than Sis and Ges clusters. Among all clusters investigated, Si₂Ge₄, Si₂Ge5, Si₂Ge6, Si6Ge₃, Si5Ge5, Si7Ge₄, Si₃Ge9, and Si8Ge5 clusters have the relatively lower mixing energies and thus the highest energetic stabilities. Moreover, the Si₂Ge₄, Si₂Ge6, Si5Ge5, Si7Ge₄, and Si8Ge5 clusters with higher HOMO-LOMO gaps should have higher chemical stabilities than the same-sized Sis and Ges clusters. The Si5Ge5 cluster has a higher ionization potential than Si10 and Ge10. At the size s = 13, the geometry with the highest symmetry has the highest energetic and chemical stabilities.

Computational study of GanAsm (m + n = 2–9) clusters using DFT calculations

Gallium arsenide is a semiconductor compound with well-known properties in its bulk phase. Theoretical works explain some of the properties of this material at a cluster scale; nevertheless, more research is required to fully understand these systems. In this work, we used the density functional theory (DFT) formalism, specifically the PBE functional and the TZ2P basis set for the study of structural, electronic, and chemical properties of GanAsm (m + n = 2–9) clusters in the gas phase, for all possible compositions. Our study reveals that the structural and electronic properties in GanAsm clusters present a size and composition dependence, with a size range within 3–10 A. Even/odd behavior is observed in most electronic and chemical properties of the clusters. The even/odd behavior is related to the electronic close shell structure of the system. It is found that the predominance of arsenic atoms in the GanAsm clusters generate comparatively more stable molecules, with lower binding energies per atom, higher hardness values, ionization potentials, and GapHOMO-LUMO.

Systematic study on the structures and properties of (Ag2S)n (n = 1-8) clusters.

Silver sulfide is a famous semiconductor, which can be used in many areas. Understanding the size evolution of silver sulfide clusters is useful in controlling their size to improve their properties in applications. The structures of (Ag2S)n (n = 1-8) clusters are explored using a combined method of genetic algorithm (GA) and density functional theory (DFT). The TPSSh/def2-tzvp(Ag)/6-311G(d)(S) method has been used to optimize the structures. The re-optimized structures and refined energies are computed at PBE0/Lanl2tz(Ag)/6-311G(d,p)(S) level according to the benchmark calculations. The global minimum (GM) structures, HOMO and LUMO frontier orbitals, density of states, ionization potentials, electron affinity energies, noncovalent interactions, and natural populations of the clusters have been studied. The clusters evolve from open to cage structures when n varies from 1 to 8. A triangular Ag3S3 unit is found to be an important building block, which can construct the global minimum structures of (Ag2S)n (n = 3-8) clusters. When n > 6, quadrangular Ag4S4 rings present in (Ag2S)n clusters. (Ag2S)6 and (Ag2S)8 clusters are in hollow conformation, and both of which have special stability because of their high HOMO-LUMO gaps, high ionization potentials, and Ag⋯Ag attractive interactions in them. Graphical abstract.

Astrophysical detection of the helium hydride ion HeH.

During the dawn of chemistry1,2, when the temperature of the young Universe had fallen below some 4,000 kelvin, the ions of the light elements produced in Big Bang nucleosynthesis recombined in reverse order of their ionization potential. With their higher ionization potentials, the helium ions He2+ and He+ were the first to combine with free electrons, forming the first neutral atoms; the recombination of hydrogen followed. In this metal-free and low-density environment, neutral helium atoms formed the Universe's first molecular bond in the helium hydride ion HeH+ through radiative association with protons. As recombination progressed, the destruction of HeH+ created a path to the formation of molecular hydrogen. Despite its unquestioned importance in the evolution of the early Universe, the HeH+ ion has so far eluded unequivocal detection in interstellar space. In the laboratory the ion was discovered3 as long ago as 1925, but only in the late 1970s was the possibility that HeH+ might exist in local astrophysical plasmas discussed4-7. In particular, the conditions in planetary nebulae were shown to be suitable for producing potentially detectable column densities of HeH+. Here we report observations, based on advances in terahertz spectroscopy8,9 and a high-altitude observatory10, of the rotational ground-state transition of HeH+ at a wavelength of 149.1 micrometres in the planetary nebula NGC7027. This confirmation of the existence of HeH+ in nearby interstellar space constrains our understanding of the chemical networks that control the formation of this molecular ion, in particular the rates of radiative association and dissociative recombination.

Synthesis and Antiplatelet Potential Evaluation of 1,3,4-Oxadiazoles Derivatives

Abstract A novel series of 2-(3-methyl-1,6-diphenyl-1H-pyrazolo[3,4-b]pyridin-4-yl)-5-aryl-1,3,4-oxadiazoles (4a–4h) has been synthesized from corresponding hydrazones (3a–3h) and evaluated their antiplatelet aggregation effect induced by arachidonic acid and collagen. Spectral data and elemental evaluation were used to confirm the structure of the compounds while molecular docking against cyclooxygenase 1 and 2 (COX1 & COX2) and quantitative structure-activity relationship (QSAR) were performed in describing their antiplatelet potential. All synthesized compound exhibited more than 50% platelet aggregation inhibition against both arachidonic acid and collagen. Antiplatelet activities results showed that 4b and 4f compounds have highest % inhibition against arachidonic acid. High Egap and ionization potential values showed that the compound 4d, 4e and 4f were supposed to be more active and good electron donor while 4b, 4c, 4d, 4e, 4g and 4h might be more active due to more electrophilic sites. Interaction with more than one residues in the binding pocket of COX-1 in comparison with aspirin and ligand efficacy (LE) consequences showed that compounds have excellent action potential for COX-1. Computational evaluations are in good agreement with antiplatelet activities of the compounds. All compounds might be promising antiplatelet agents especially 4b, 4f and helpful in the synthesis of new drugs for the treatment of cardiovascular diseases (CVDs).

Helium Suppression in Impulsive Solar Energetic-Particle Events

We have studied the element abundances and energy spectra of the small "He-poor" impulsive solar energetic-particle (SEP) events, comparing them with other impulsive SEP events with more-normal abundances of He. He-poor events can have abundances as low as He/O ~ 2, while both impulsive and gradual SEP events usually have source abundances of 30 < He/O < 100 with mean values of 50 - 60. He/C ratios are not only low, but often decrease with energy in He-poor events. Abundance enhancement patterns of other elements with atomic numbers 6 < Z < 56, and likely values of their mass-to-charge ratios A/Q, are generally unaltered in He-poor events, as are the probable source-plasma temperatures of 2.5 - 3.2 MK for all impulsive SEP events. One He-poor event is also an example of a rarer C-poor event with C/O = 0.08 +- 0.04, sup-pressed by a factor over 5 from the mean. We discuss suggestions of a possible A/Q threshold during acceleration and of the sluggish ionization of He entering the corona, because of its uniquely high first ionization potential (FIP), but the suppression of He and the decline of He/C with energy is difficult to explain if both He and C are fully ionized with A/Q = 2 as expected at 2.5 - 3.2 MK. Although less dramatic, a possible excess enhancement of Ne in some impulsive SEP events is also considered. Possible causes of the large ~30% spectral and abundance variations in impulsive events are also discussed. However, the physics of the He-poor events remains a mystery.