Difference In Ionization Potential Research Articles

Theoretical Photoelectron Spectroscopy of Quadruple-Bonded Dimolybdenum(II,II) and Ditungsten(II,II) Paddlewheel Complexes: Performance of Common Density Functional Theory Methods.

We have revisited the gas-phase photoelectron spectra of quadruple-bonded dimolybdenum(II,II) and ditungsten(II,II) paddlewheel complexes with modern density functional theory methods and obtained valuable calibration of four well-known exchange-correlation functionals, namely, BP86, OLYP, B3LYP*, and B3LYP. All four functionals were found to perform comparably, with discrepancies between calculated and experimental ionization potentials ranging from <0.1 to ∼0.5 eV, with the lowest errors observed for the classic pure functional BP86. All four functionals were found to reproduce differences in ionization potentials (IPs) between analogous Mo2 and W2 complexes, as well as large, experimentally observed ligand field effects on the IPs, with near-quantitative accuracy. The calculations help us interpret a number of differences between analogous Mo2 and W2 complexes through the lens of relativistic effects. Thus, relativity results in not only significantly lower IPs for the W2 complexes but also smaller HOMO-LUMO gaps and different triplet states relative to their Mo2 counterparts.

A DFT approach towards understanding the thermal stability of TKX-50 and their key precursors through band gaps and MESP.

TKX-50 (dihydroxylammonium 5,5'-bistetrazolate-1,1'-dioxide) is a recent time invention by Klapotke et. al. in the field of high energy materials, and it outperforms all the existing materials by means of performance parameters. It is rising as potential energetic material due to favorable thermal insensitivity, low toxicity and safe handling. The decomposition temperature (Tmax) values of precursors such as glyoxime (I), 1,2-dichloroglyoxime (II), 1,2-diazidoglyoxime (III), and bistetrazoledihydroxide (IV) and ending products TKX-50 (V) and ABTOX (VI) have been attempted to correlate with the results obtained from molecular electrostatic potentials and band gaps calculated from the difference of ionization potential and electron affinity. The molecular electrostatic potential values of azido attached -NO group of III are much less than that of hydro/chloro attached -NO group of I/II and that of tetrazole groups IV, V, and VI. The band gaps calculated from stability trend in the increasing order of III < II < I < IV < V < VI are well corroborated with stability trend drawn from experimentally determined decomposition temperatures. Further, employing conceptual density functional theory (DFT) molecular descriptors, band gap values were calculated via the difference of ionization potential and electron affinity to understand the thermal stability of TKX-50, ABTOX, and its precursors.

Interfaces between Pb-Free Double Perovskite Cs2NaBiI6 and MXenes Sc2CO2 and Sc2C(OH)2.

First-principles calculations are used to explore the electronic properties of the interfaces between the Pb-free double perovskite Cs2NaBiI6 and the MXenes Sc2CO2 and Sc2C(OH)2. The effect of the termination group on the stability, ionization potential, electron affinity, and band alignment is investigated. We find a type II band alignment at the Cs2NaBiI6/Sc2CO2 interface, which permits charge transfer, and a type III band alignment at the Cs2NaBiI6/Sc2C(OH)2 interface, which results in electron-hole recombination. Sc2CO2 turns out to be highly promising for solar cell applications due to an almost ideal ionization potential difference to Cs2NaBiI6.

Comparing Isoelectronic, Quadruple-Bonded Metalloporphyrin and Metallocorrole Dimers: Scalar-Relativistic DFT Calculations Predict a >1 eV Range for Ionization Potential and Electron Affinity.

A scalar-relativistic DFT study of isoelectronic, quadruple-bonded Group 6 metalloporphyrins (M = Mo, W) and Group 7 metallocorroles (M = Tc, Re) has uncovered dramatic differences in ionization potential (IP) and electron affinity (EA) among the compounds. Thus, both the IPs and EAs of the corrole derivatives are 1 eV or more higher than those of the porphyrin derivatives. These differences largely reflect the much lower orbital energies of the δ- and δ*-orbitals of the corrole dimers relative to those of the porphyrin dimers, which in turn reflect the higher (+III as opposed to +II) oxidation states of the metals in the former compounds. Significant differences have also been determined between Mo and W porphyrin dimers and between Tc and Re corrole dimers. These differences are thought to largely reflect greater relativistic destabilization of the 5d orbitals of W and Re relative to the 4d orbitals of Mo and Tc. The calculated differences in IP and EA should translate to major differences in electrochemical redox potentials-a prediction that in our opinion is well worth confirming.

Electronic structure and stability of the (0 0 1) surface of halide double perovskite Cs2AgBiBr6

Cs2AgBiBr6 is an attractive lead-free candidate for photovoltaic applications. Recently, surfaces were reported to be crucial in improving the power conversion efficiency of Cs2AgBiBr6-based perovskite solar cells (PSCs). However, the in-depth understanding of the stability and electronic structure of Cs2AgBiBr6 surfaces is still lacking. To address it, we explore the energetics and electronic properties of the Cs2AgBiBr6 (001) surface with CsBr and AgBiBr4 terminations by first-principles calculations. It is found that both terminations may coexist on the (001) surface. Importantly, a lack of deep-states assisted carrier recombination and the low probability of the band-edges related nonradiative recombination for the (001) surface may contribute to the long lifetime of carriers observed in Cs2AgBiBr6. Besides, the moderate carrier effective masses of the (001) surface explain the experimental moderate charge-carriers mobility of Cs2AgBiBr6. Encouragingly, there is a considerable difference in ionization potentials for the two terminations, implying that surface/interface engineering can modify the band offset between the light absorber and carrier transporter and shows the potential to improve charge transfer. Our research provides valuable insights into the photoelectric properties of the Cs2AgBiBr6 (001) surface. It is vital for the future design of Cs2AgBiBr6 PSCs through surface/interface engineering.

Boosting Nitrogen Activation via Bimetallic Organic Frameworks for Photocatalytic Ammonia Synthesis

Photocatalytic ammonia synthesis from N2 is a carbon-neutral strategy, although its efficiency is impeded by the activation of inert N≡N triple bonds. In N2 activation, the electron acceptance process is often strongly coupled with the electron donation process, leading to a high potential activation energy barrier and low photocatalytic activity. Herein, we proposed a strategy to decouple these two processes by bimetallic organic frameworks (BMOFs) for boosting N2 activation. The rationally designed BMOFs are composed of two functional metal nodes, in which the hard acid metal node with a high ionization potential (In) accepts the electron from N2 and the soft acid metal node with a low In donates the electron to N2. Owing to the bimetal synergistic effect, the potential activation energy barrier of N2 is reduced, as confirmed by the in situ Fourier transform infrared (FTIR) spectra and density functional theory (DFT) calculations. Via testing six kinds of bimetal combinations, it is found that, as the ionization potential difference (ΔIn) between the two metals is ≥6 eV and the proportion of high In metal reaches ∼20%, the bimetal synergistic effect becomes dominant. In all the as-prepared BMOFs, the optimal BMOF(Sr)–0.2Fe photocatalyst exhibits an NH3 evolution rate up to 780 μmol g–1 h–1. This work may unveil a corner of the hidden mechanism for the chemical bond activation in a broad range of catalytic processes.

Dynamic interference of the high harmonics from photoisomerizing 1,3-cyclohexadiene

The ionization potential difference between photoexcited and ground-state molecules results in a phase difference between their high harmonics, which causes high harmonic interference. The interference enables us to reveal how ionization potential of the photoexcited molecules evolves along the electronic relaxation path from the Franck–Condon state to the electronic ground state. We observe the ultrafast electron dynamics of a photoisomerizing molecule, 1,3-cyclohexadiene, via high harmonic interference. The experimental observations reveal that the electronic relaxation of 1,3-cyclohexadiene takes 200 fs, and the photoisomerization to 1, 3, 5-hexatriene takes an additional 450 fs.

Near infrared characteristics of air plasma induced by nanosecond laser

The near infrared emission from laser induced air plasma has been investigated in a range of 1100–2400 nm. The infrared spectra of air plasma consist of linear spectral and continuum radiation. Most of the spectral features observed are identified, including atomic lines of O I and N I and molecular bands of N&lt;sub&gt;2&lt;/sub&gt;. The spectra show trace of blackbody background emission and the plasma temperature is estimated from Planck law. We find that the continuum radiation is mainly origins mainly from the blackbody emission of plasma. There is a limitation of plasma temperature estimation by using Boltzmann method. For example, the local thermodynamic equilibrium must be satisfied, and the trend of change in plasma temperature can be estimated within a few microseconds after the laser shot. In this paper, the plasma temperature in 15 μs after laser irradiation is estimated from the Planck law, and the temperature of air plasma is estimated to be about 3900 K, which can compensate for the shortcomings of Boltzmann method. It is found that the neutral atomic spectra of N and O both may contribute to the radiation of the air plasma at 1128 nm. Then we keep the air pressure in the vacuum chamber at 80 kPa, and change the nitrogen and oxygen content in the chamber. The infrared spectrum data show that the oxygen content in the mixed gas only affect the radiation of 1128 nm wavelength. The binary linear regression analysis shows that oxygen contributes much to the radiation of 1128 nm wavelength. This can be explained by the difference in ionization potential between molecule O&lt;sub&gt;2&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;. The infrared radiation intensities of the air plasma at 1128 nm under 20−80 kPa are obtained, and they are compared with the calculated results obtained with the fitting formula. The predicted value is very close to the experimental value and the relative error is negligibly at the pressure of 30−80 kPa. The study of the characteristics of infrared emission from laser induced plasma is of great significance for understanding and using the physical mechanisms of laser-matter interaction.

Role of anions in radiation-induced transformations of 18-crown-6 complexes with barium salts: simulating the effects of extraction mechanism on radiation stability of macrocyclic extractants

Complexes of 18-crown-6 with BaCl2, Ba(NO3)2 and Ba(NTf2)2 salts were synthesized and irradiated with X-rays to simulate the radiation degradation of a macrocyclic component of extractants based on crown ether solutions in commonly used solvents. Structures and post-irradiation transformations of radical products stabilized in these complexes at 77 K were studied using EPR spectroscopy, and the mechanism of their formation and decay was proposed. Differences in ionization potentials of the macrocycle and the anions and reactivity of the intermediates generated from the anions are of importance for radiation stability of the studied compounds. The nitrate-anions was demonstrated to protect 18C6 from destruction whereas Cl− and bis(trifluoromethylsulfonyl)imide-anions can impair the radiation stability of the macrocycle. The results of the present study offer an opportunity to predict the radiation stability of the crown ether extractants and their applicability for liquid radioactive waste reprocessing.

Odd-Electron Bonds.

The history and theory of one- and three-electron bonds are presented and discussed. It is shown that the dependence of the odd-electron bond energy on the difference in ionization potentials of the bonding partners must be corrected to include the ion-pairing energy for neutral odd-electron bonded complexes.

Linewidth Pressure Measurement: A New Technique for High Vacuum Characterization

Pressure measurement is often the limiting factor in the accuracy of quantitative ion-molecule experiments. We present a new method for pressure measurement based on analysis of pressure-limited Fourier transform ion cyclotron resonance (FTICR) linewidths for well-characterized collisions of Ar(+) with Ar. The kinetic energy dependence of Ar(+)/Ar collision cross sections is well-described using a single-parameter fitting procedure, which results in pressure measurements in good agreement with those from a cold cathode tube and from measurement of total ion signal following electron impact ionization. The new method avoids problems inherent in ionization-based methods, such as those arising from differences in ionization potential or perturbations to the pressure that occur during electron ionization of the gas to be measured, and should be applicable in the trapping cells of FTICR and Orbitrap mass spectrometers.

Effect of Donor-Acceptor Substitution on Optoelectronic Properties of Conducting Organic Polymers.

The impact of donor-acceptor substitution on optical and electronic properties of conducting polymers was investigated with time-dependent density functional theory (TDDFT). A series of donor-acceptor systems with thiophene, 3,4-ethylenedioxythiophene, and pyrrole as donors and 3,4-difluorothiophene, diketopyrrolopyrrole, 2,1,3-benzothiadiazole, 4-dicyanomethylene-4H-cyclopenta[2,1-b;3,4-b']dithiophene, and indeno[1-2b]-fluorene-6,12-dimalonitrile as acceptors as examples of donor-acceptor systems with increasing donor-acceptor character was studied. Spectral properties were analyzed in terms of differences in ionization potentials and electron affinities of donors and acceptors, charge separations between donors and acceptors in ground and excited states, and electron distribution in the acceptor units. A shift in electron density away from the backbone caused by some of the acceptors correlates with localization of the conduction band on the acceptor. Localization does not correlate with energy level differences between donor and acceptor. Localization results in shift of oscillator strength from the HOMO-LUMO peak to a higher energy feature where the first delocalized orbital acts as the acceptor. The "camel back" absorption with two equally strong peaks that gives rise to green polymers is the intermediate case associated with partial localization of the conduction band. Stronger localization causes the HOMO-LUMO band to almost vanish.

First-principles study of valence band offsets at ZnSnP2/CdS, ZnSnP2/ZnS, and related chalcopyrite/zincblende heterointerfaces

The valence band offsets of chalcopyrite ZnSnP2 (ZSP), CdSnP2 (CSP), CuInSe2 (CIS), and CuGaSe2 (CGS) against zincblende CdS and ZnS are obtained using first-principles calculations based on hybrid density functional theory. The ZSP-CSP (ZCSP) alloy is isostructural to the CIS-CGS (CIGS) alloy and is known for its potential usage in photovoltaic applications. Therefore, the band offsets with other semiconductors, such as CdS and ZnS, are important. The calculated valence band offsets are ∼1.0 eV for ZSP/CdS and CSP/CdS, ∼1.2 eV for ZSP/ZnS and CSP/ZnS, ∼1.2 eV for CIS/CdS and CGS/CdS, and ∼1.3 eV for CIS/ZnS and CGS/ZnS. The CdS/ZnS valence band offset is within 0.1 eV. Transitivity of natural valence band offsets in the investigated semiconductors holds within ∼0.1 eV, which is smaller than the error in band alignment of ∼0.2 eV when ionization potential differences are used. The ZSP-CSP and CIS-CGS systems have similar valence and conduction band positions, which is an important piece of information for band offset engineering in the development of photovoltaics using ZCSP alloys.

Band offsets of CuInSe2/CdS and CuInSe2/ZnS (110) interfaces: A hybrid density functional theory study

The valence band offsets of the CuInSe${}_{2}$/CdS and CuInSe${}_{2}$/ZnS (110) interfaces are obtained based on various definitions using first-principles calculations in the framework of hybrid density functional theory. Both the strained band offset and the unstrained, or natural, band offset are investigated, where the two phases share and do not share in-plane lattice parameters perpendicular to the stacking direction, respectively. The valence band offset is determined by first obtaining the difference between the reference levels of two phases in the regions far from the interface and then adding the difference between the valence band maximum and the reference levels of bulk for the two phases. The nonfaceted (110) interface and a number of (112)/(11$\overline{2}$) faceted interfaces, some containing ordered point defects in the CuInSe${}_{2}$ (CIS) region, are considered. The excess energies of CIS/CdS and CIS/ZnS interfaces are lower when there are no ordered point defects, in contrast to the CIS surfaces that stabilize with ordered defect formation. The valence band offset is not significantly dependent on the atomic configurations at the interface as long as there are no charged layers. Surface calculations suggest that the reference level, which is determined by the average electrostatic potential at the atomic site, is not strongly dependent on lattice strain. A definition of the natural valence band offset that assumes a strain-invariant difference in the reference levels of the two phases provides values almost independent of the in-plane lattice parameters used in the interface calculation, which are about $\ensuremath{-}$1.2 and $\ensuremath{-}$1.3 eV with respect to CIS for the CIS/CdS and CIS/ZnS interfaces that contain no charged layers, respectively. The ionization potential difference can differ from the natural valence band offset by up to 0.3 eV without any consistent tendency to overestimate or underestimate, showing that the ionization potential difference is not necessarily a reasonable measure of the natural valence band offset.

Sequence and conformation effects on ionization potential and charge distribution of homo-nucleobase stacks using M06-2X hybrid density functional theory calculations

DNA is subject to oxidative damage due to radiation or by-products of cellular metabolism, thereby creating electron holes that migrate along the DNA stacks. A systematic computational analysis of the dependence of the electronic properties of nucleobase stacks on sequence and conformation was performed here, on the basis of single- and double-stranded homo-nucleobase stacks of 1–10 bases or 1–8 base pairs in standard A-, B-, and Z-conformation. First, several levels of theory were tested for calculating the vertical ionization potentials of individual nucleobases; the M06-2X/6-31G∗ hybrid density functional theory method was selected by comparison with experimental data. Next, the vertical ionization potential, and the Mulliken charge and spin density distributions were calculated and considered on all nucleobase stacks. We found that (1) the ionization potential decreases with the number of bases, the lowest being reached by Gua≡Cyt tracts; (2) the association of two single strands into a double-stranded tract lowers the ionization potential significantly (3) differences in ionization potential due to sequence variation are roughly three times larger than those due to conformational modifications. The charge and spin density distributions were found (1) to be located toward the 5′-end for single-stranded Gua-stacks and toward the 3′-end for Cyt-stacks and basically delocalized over all bases for Ade- and Thy-stacks; (2) the association into double-stranded tracts empties the Cyt- and Thy-strands of most of the charge and all the spin density and concentrates them on the Gua- and Ade-strands. The possible biological implications of these results for transcription are discussed.

Metastability of Free Cobalt and Iron Clusters: A Possible Precursor to Bulk Ferromagnetism

Homonuclear cobalt and iron clusters Co(N) and Fe(N) measured in a cryogenic molecular beam exist in two states with distinct magnetic moments (μ), polarizabilities, and ionization potentials, indicating distinct valences. The μ is approximately quantized: μ(N)∼2Nμ(B) in the ground states and μ(N)(*)∼Nμ(B) in the excited states for Co; μ(N)∼3Nμ(B) and μ(N)(*)∼Nμ(B) for Fe. At a large size, the average μ of the two states converges to the bulk value with diminishing ionization potential differences. The experiments suggest localized ferromagnetism in the two states and that itinerant ferromagnetism emerges from their superposition.

Raman Spectroscopy of the Reaction of Thin Films of Solid-State Benzene with Vapor-Deposited Ag, Mg, and Al

Thin films of solid-state benzene at 30 K were reacted with small quantities of vapor-deposited Ag, Mg, and Al under ultrahigh vacuum, and products were monitored using surface Raman spectroscopy. Although Ag and Mg produce small amounts of metal–benzene adduct products, the resulting Raman spectra are dominated by surface enhancement of the normal benzene modes from metallic nanoparticles suggesting rapid Ag or Mg metallization of the film. In contrast, large quantities of Al adduct products are observed. Vibrational modes of the products in all three systems suggest adducts that are formed through a pathway initiated by an electron transfer reaction. The difference in reactivity between these metals is ascribed to differences in ionization potential of the metal atoms; ionization potential values for Ag and Mg are similar but larger than that for Al. These studies demonstrate the importance of atomic parameters, such as ionization potential, in solid-state metal–organic reaction chemistry.

Effects of heterole spacers on the structural, optical, and electrochemical properties of 2,5‐bis(1,5‐diphenylphosphol‐2‐yl)heteroles

Abstract2,5‐Bis(1,5‐diphenylphosphol‐2‐yl)he‐terole derivatives were prepared via Pd‐catalyzed Stille‐type cross‐coupling reactions of α‐(tributylstannyl) phosphole or α‐iodophosphole with the corresponding 2,5‐difunctionalized heteroles (pyrrole, furan, and thiophene). X‐ray crystallographic analyses of three σ4‐P derivatives have elucidated that the coplanar phosphole‐heterole‐phosphole π‐networks are constructed in both anti–anti and syn–anti conformations. In the case of the pyrrole‐linked σ4‐P derivatives, there is a weak hydrogen‐bonding interaction between NH and P=X (X = O, S) groups. The optical and electrochemical properties of the σ3‐P and σ4‐P=O derivatives were revealed experimentally by means of UV–vis absorption/emission spectroscopy and cyclic/differential pulse voltammetry. In all the heterole‐linked derivatives, the P‐oxidation lowers LUMO levels more efficiently than HOMO levels and, as a result, narrows HOMO–LUMO gaps. In each series (σ3‐P or σ4‐P=O), the lowest π–π* transition energies of the phosphole–heterole–phosphole π‐systems were found to decrease in the following order: thiophene &gt; furan &gt; pyrrole, and their electrochemical oxidation and reduction potentials shift to the negative side in the same order. These results basically reflect the differences in ionization potential and electron affinity of the central heterole spacers. Density functional theory calculations on the model compounds supported the experimentally observed results. The HOMO of the molecule resides on the conjugated polyene network of the π‐system, whereas the LUMO is strongly located on the phosphole subunits. The present comparative study demonstrates, for the first time, that the intriguing electronic structures and the fundamental properties of the 2,5‐bis(1,5‐diphenylphosphol‐2‐yl)heteroles can be finely tuned by simple selection of the appropriate heterole spacer. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:457–470, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20708

Injection and Trapping of Tunnel-Ionized Electrons into Laser-Produced Wakes

A method, which utilizes the large difference in ionization potentials between successive ionization states of trace atoms, for injecting electrons into a laser-driven wakefield is presented. Here a mixture of helium and trace amounts of nitrogen gas was used. Electrons from the K shell of nitrogen were tunnel ionized near the peak of the laser pulse and were injected into and trapped by the wake created by electrons from majority helium atoms and the L shell of nitrogen. The spectrum of the accelerated electrons, the threshold intensity at which trapping occurs, the forward transmitted laser spectrum, and the beam divergence are all consistent with this injection process. The experimental measurements are supported by theory and 3D OSIRIS simulations.

Charge carrier photogeneration and hole transport properties of blends of a π-conjugated polymer and an organic-inorganic hybrid material

This study examined the charge carrier photogeneration and hole transport properties of blends of poly (9-vinylcarbazole) (PVK), a π-conjugated polymer, with different weight proportions (0~29.4 wt%) of (PEA)-VOPO4·H2O (PEA: phenethylammonium cation), a novel organic-inorganic hybrid material, using IR, UV-Vis, and energy dispersive spectroscopy (EDS), thermogravimetric analysis (TGA), steady state photocurrent (SSPC) measurement, and atomic force microscopy (AFM). The SSPC measurements showed that the photocurrent of PVK was reduced by approximately three orders of magnitude by the incorporation of a small amount (~12.5 wt%) of (PEA) VOPO4·H2O, suggesting that hole transport occurred through the PVK carbazole groups, whereas a reverse trend was observed at high proportions (>12.5 wt%) of (PEA)VOPO4·H2O, suggesting that transport occurred via (PEA)VOPO4·H2O molecules. The transition to a trap-controlled hopping mechanism was explained by the difference in ionization potential and electron affinity of the two compounds as well as the formation of charge percolation threshold pathways.