Adiabatic Electron Affinity Research Articles

Ab initio investigation of 2,2′‐bis(4‐trifluoromethylphenyl)‐5,5′‐bithiazole for the design of efficient organic field‐effect transistors

The initial molecular structure of 2,2′‐bis(4‐trifluoromethylphenyl)‐ 5,5′‐bithiazole has been optimized in the ground state using density functional theory (DFT). The distribution patterns of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) have also been evaluated. To shed light on the charge transfer properties, we have calculated the reorganization energy of electron λe, the reorganization energy of hole λh, adiabatic electron affinity (EAa), vertical electron affinity (EAv), adiabatic ionization potential (IPa), and vertical ionization potential (IPv) using DFT. Based on the evaluation of hole reorganization energy, λh, and electron reorganization energy, λe, it has been predicted that 2,2′‐bis(4‐trifluoromethylphenyl)‐5,5′‐bithiazole would be a better electron transport material. Finally, the effect of electric field on the HOMO, LUMO, and HOMO–LUMO gap were observed to check its suitability for the use as a conducting channel in organic field‐effect transistors. © 2015 Wiley Periodicals, Inc.

Samarium doped silicon clusters SmSin (n = 3–10) and their anions: Structures, thermochemistry, electron affinities, and magnetic moments

The structures, adiabatic electron affinities (AEAs), dissociation energies (DEs), hardness, and magnetic moments of SmSin (n=3–10) and their anions were examined by means of B2PLYP, TPSSh, PBE0 and B3LYP methods. Basis sets adopted are of segmented (SEG) Gaussian valence basis sets and relativistic small-core effective potentials (ECP) with additional diffuse 2dfg functions, denoted aug-SEG/ECP for Sm atoms and aug-cc-pVTZ for Si atoms. The most stable structures can be viewed as replacing a Si of the ground-state structure of Sin+1 with a Sm atom. The theoretical AEAs are in excellent agreement with experimental data, especially the AEAs at B2PLYP and TPSSh levels. The average absolute errors from experiment are by 0.04, 0.06, 0.10 and 0.11eV at the B2PLYP, the TPSSh, the PBE0 and the B3LYP levels, respectively. The DEs of Sm from SmSin (n=3–10) and their anions were estimated to examine their relative stabilities. Natural population analysis (NPA) reveals that the Sm atom in all the neutral and anionic clusters acts as an electron donor. Hardness analysis reveals that doping Sm atom to Sin (n=3–10) clusters raises the photochemical sensitivity. Analysis of magnetic moments reveals that the total magnetic moments are contributed by Samarium atom.

Probing electronic states of TaC and observation of a stable excited state ofTaC−by anion-photoelectron spectroscopy

We report the experimental value of electron affinity for TaC to be 1.928(0.056) eV by performing photodetachment of its anion at 355 nm. An excited-electronic state of the anion, stable against autodetachment, is observed lying 0.828 eV above the ground-electronic state. Five low-lying electronic states of TaC are observed and identified by comparison with restricted second-order configuration interaction (SOCI) calculations. Vibrational frequencies for the electronic states are obtained from the analysis of the measured data. We also present the results of density functional theory (DFT) calculations performed on the adiabatic electron affinity, yielding a value of 1.9236 eV and vertical detachment energy value of 1.924 eV.

Benzonitrile: Electron affinity, excited states, and anion solvation.

We report a negative-ion photoelectron imaging study of benzonitrile and several of its hydrated, oxygenated, and homo-molecularly solvated cluster anions. The photodetachment from the unsolvated benzonitrile anion to the X̃(1)A1 state of the neutral peaks at 58 ± 5 meV. This value is assigned as the vertical detachment energy (VDE) of the valence anion and the upper bound of adiabatic electron affinity (EA) of benzonitrile. The EA of the lowest excited electronic state of benzonitrile, ã(3)A1, is determined as 3.41 ± 0.01 eV, corresponding to a 3.35 eV lower bound for the singlet-triplet splitting. The next excited state, the open-shell singlet Ã(1)A1, is found about an electron-volt above the triplet, with a VDE of 4.45 ± 0.01 eV. These results are in good agreement with ab initio calculations for neutral benzonitrile and its valence anion but do not preclude the existence of a dipole-bound state of similar energy and geometry. The step-wise and cumulative solvation energies of benzonitrile anions by several types of species were determined, including homo-molecular solvation by benzonitrile, hydration by 1-3 waters, oxygenation by 1-3 oxygen molecules, and mixed solvation by various combinations of O2, H2O, and benzonitrile. The plausible structures of the dimer anion of benzonitrile were examined using density functional theory and compared to the experimental observations. It is predicted that the dimer anion favors a stacked geometry capitalizing on the π-π interactions between the two partially charged benzonitrile moieties.

Negative ion properties of trans 2,2',6,6'-tetrafluoroazobenzene: Experiment and theory.

Chemical bonding and the electronic structure of the trans 2,2',6,6'-tetrafluoroazobenzene negative ion have been studied using collision-induced dissociation as well as photodetachment-photoelectron spectroscopy and the experimental results for different properties were compared with the corresponding values calculated using ab initio quantum chemistry methods. The trans 2,2',6,6'-tetrafluoroazobenzene anion was prepared by atmospheric pressure chemical ionization for the collision induced dissociation (CID) experiment and through thermal electron attachment in the photodetachment-photoelectron spectroscopy experiments. The adiabatic electron affinity of trans 2,2',6,6'-tetrafluoroazobenzene was measured to be 1.3 ± 0.10 eV using 355 nm, 488 nm, and 532 nm photodetachment photons and the vertical detachment energy was measured to be 1.78 ± 0.10 eV, 2.03 ± 0.10 eV, and 1.93 ± 0.10 eV, respectively. The adiabatic electron affinity was calculated employing different ab initio methods giving values in excellent agreement with experimental results. Energy resolved collision induced dissociation experiment study of the precursor anion resulted in 1.92 ± 0.15 eV bond dissociation energy for the collision process yielding [C6H3F2](-) fragment ion at 0 K. Calculations using different ab initio methods resulted in a bond dissociation energy ranging from 1.79 to 2.1 eV at 0 K. Two additional CID fragment ions that appear at higher energies, [C6H2F](-) and [C6H](-), are not results of a single bond cleavage. The occurrence of [C6H](-) is of particular interest since it is the first anion to be observed in the interstellar medium.

Ytterbium doped silicon clusters YbSin (n = 4–10) and their anions: Structures, thermochemistry, and electron affinities

The structures, electron affinities, dissociation energies, hardness, and dipole moments of YbSin (n=4–10) and their anions were examined using B3LYP, TPSSh, PBE and wB97X methods. The lowest-energy structures can be regarded as replacing a Si of the ground-state structure of Sin+1 with a Yb atom. The theoretical adiabatic electron affinities (AEAs) of YbSin are in excellent agreement with experimental data. The average absolute errors from experiment are by 0.08, 0.07, 0.05 and 0.08eV at the B3LYP, the TPSSh, the PBE and the wB97X levels, respectively. Theoretical AEAs of 2.33±0.05eV for YbSi9 are more reliable than the experimental value of 2.60±0.05eV. The hardness analysis reveals that doping Yb atom to Sin (n=4–10) clusters raises the photochemical sensitivity. The dissociation energies of Yb atom from YbSin and their anions were calculated to examine relative stabilities.

Franck-Condon simulation of the anion photoelectron spectroscopy of CrO2 by coherent state method

The equilibrium geometries and harmonic vibrational frequencies of CrO2(X3B1) and CrO2-(X4B1) were calculated using density functional theory and couple cluster method with various basis sets. A program was developed to calculate multidimensional Franck-Condon factors based on coherent state method. Its application to the photoelectron spectroscopy of the CrO2(X3B1)←CrO2-(X4B1) photodetachment process was presented. The simulation at the CCSD(T)/aug-cc-pwCVTZ level of theory is in good agreement with the experimental spectroscopy, revealing that the hot bands contribute to the spectroscopy remarkably. All peaks of the experimental spectroscopy were assigned explicitly according to the theoretical modeling. Our calculations support original experimental assignments. In addition, the agreement between the calculated and experimental adiabatic electron affinities of CrO2(X3B1) is excellent.

Structural, spectroscopic and energetic parameters of P-bearing species having astrophysical importance

AbstractMolecular parameters such as equilibrium structure, dipole moment, rotational constant, harmonic frequency, IR intensity, adiabatic electron affinity, atomisation energy and ionisation potential of some P-bearing molecules PS, PO and HC3P in their neutral, cationic and anionic forms were investigated using the popular B3LYP hybrid density functional with four basis sets 6-311++G(2df,2pd), 6-311++G(3df,3pd), cc-pVTZ and aug-cc-pVTZ. The computed data conform well to those existing in the literature. Therefore, the predicted data for those molecules or ions which are not available in the literature should be reliable.

Photoelectron spectrum of PrO(-).

The photoelectron (PE) spectrum of PrO(-) exhibits a short 835 ± 20 cm(-1) vibrational progression of doublets (210 ± 30 cm(-1) splitting) assigned to transitions from the 4f(2) [(3)H4] σ6s (2) Ω = 4 anion ground state to the 4f(2) [(3)H4] σ6s Ω = 3.5 and 4.5 neutral states. This assignment is analogous to that of the recently reported PE spectrum of CeO(-), though the 82 cm(-1) splitting between the 4f [(2)F2.5] σ6s Ω = 2 and Ω = 3 CeO neutral states could not be resolved [Ray et al., J. Chem. Phys. 142, 064305 (2015)]. The origin of the transition to the Ω = 3.5 neutral ground state is 0.96 ± 0.01 eV, which is the adiabatic electron affinity of PrO. Density functional theory calculations on the anion and neutral molecules support the assignment. The appearance of multiple, irregularly spaced and low-intensity features observed ca. 1 eV above the ground state cannot be reconciled with low-lying electronic states of PrO that are accessible via one-electron detachment. However, neutral states correlated with the 4f(2) [(3)H4] 5d superconfiguration are predicted to be approximately 1 eV above the 4f(2) [(3)H4] σ6s Ω = 3.5 neutral ground state, leading to the assignment of these features to shake-up transitions to the excited neutral states. Based on tentative hot band transition assignments, the term energy of the previously unobserved 4f(2) [(3)H4] σ6s Ω = 2.5 neutral state is determined to be 1840 ± 110 cm(-1).

A Frontier orbital energy approach to redox potentials

The prediction of the oxidation and reduction potentials of molecules is important in many research areas. A review of relationships obtained between frontier orbital energies (eV), the calculated ionization potentials (IP in eV), or adiabatic electron affinities (EA in eV) with the experimental oxidation and reduction potentials is presented, for selected series of β- diketones, rhodium-β-diketonato complexes, as well as metal-tris-β-diketonato complexes, with the metal Fe or Mn. The good linear relationships obtained for related series of complexes show that the oxidation and reduction potentials of these complexes can be predicted by their DFT-calculated energies.

Photoelectron spectra and structure of the Mnn(-) anions (n = 2-16).

Photoelectron spectra of the Mnn(-) anion clusters (n = 2-16) are obtained by anion photoelectron spectroscopy. The electronic and geometrical structures of the anions are computed using density functional theory with generalized gradient approximation and a basis set of triple-ζ quality. The electronic and geometrical structures of the neutral Mnn clusters have also been computed to estimate the adiabatic electron affinities. The average absolute difference between the computed and experimental vertical detachment energies of an extra electron is about 0.2 eV. Beginning with n = 6, all lowest total energy states of the Mnn(-) anions are ferrimagnetic with the spin multiplicities which do not exceed 8. The computed ionization energies of the neutral Mnn clusters are in good agreement with previously obtained experimental data. According to the results of our computations, the binding energies of Mn atoms are nearly independent on the cluster charge for n > 6 and possess prominent peaks at Mn13 and Mn13(-) in the neutral and anionic series, respectively. The density of states obtained from the results of our computations for the Mnn(-) anion clusters show the metallic character of the anion electronic structures.

Spectral signatures of semiconductor clusters: (CdSe)16 isomers

The sensitivity of several experimentally accessible properties to the geometrical structure of the semiconductor (CdSe)16 cluster is explored by density functional theory. Our test set consists of eleven (CdSe)16 isomers belonging to various topological groups. For all isomers, the UV–visible and IR spectra have been simulated and vertical and adiabatic ionization energies, adiabatic electron affinities, polarizabilities and hyperpolarizabilities have been computed. The hyperpolarizability is found to be the most sensitive property to the isomer geometrical structure followed by optical and IR spectra. This work leads to the conclusion that reliable identification of an isomer requires a combination of experimental methods.

Superhalogen properties of CoO n (n ≥ 3) species revealed by density functional theory

A systematic study on CoO n species for n = 1–5 in neutral and (mono)anionic forms has been performed using hybrid exchange-correlation functional in density functional theory. The ground-state structures are obtained, and their stabilities are analyzed against dissociation to O atom and O2 molecule. We find that Co can bind stably up to four O atoms, expanding its oxidation state to +8. The adiabatic electron affinities of CoO n and vertical detachment energies of $$ {\text{CoO}}_{n}^{ - } $$ reveal their superhalogen behavior for n ≥ 3 due to extra electron delocalization over O atoms. CoO n superhalogens can be used to form a new class of complex compounds. This idea is demonstrated by formation of stable LiCoO4 complex by interacting Li atom with CoO4 superhalogen.

Electron affinity calculation for selected PAHs using DFT: Effect of cyclopenta ring fusion and aromaticity

Quantities like adiabatic electron affinity (AEA), electron density distribution and geometry based aromaticity index are calculated for a set of polycyclic aromatic hydrocarbon (PAH) molecules. The calculated AEA values are compared with experimental values. Presence of a cyclopenta ring is observed to enhance the ability of the molecule to accommodate the extra electron in the anionic form and hence increasing the electron affinity (EA). Electrostatic potential maps and electron spin density distribution are used to analyze electron density distribution over the molecular volume in case of anions. A detailed comparison is made with the help of aromaticity index to quantify the correlation of AEA with the π-electron delocalization. A clear correlation between AEA and the aromaticity index is demonstrated. The effect of sp3 hybridized carbon atom on AEA values in PAHs is studied for the first time.

The Influence of the Terminal Phosphorothioate Diester Bond on the DNA Oxidation Process. An Experimental and Theoretical Approach.

In this study, the influence of the terminal phosphorothioate (PT) internucleotide bond in ds-DNA on the oxidation process was taken into consideration. The interaction of UV with the targeted oligonucleotide leads to an electron ejection and radical cation “hole” migration through the ds-DNA until it is trapped irreversibly in a suitable place. Phosphorothiate internucleotide bonds were detected in the bacterial genome; however, their role is still unclear. In this study a PAGE analysis of irradiated ds-DNA showed that the degradation rea ction was slowed down by the presence PT next to the anthraquinone moiety. Further, theoretical study shows that [RP] AQ-PS-dG can adopt a slightly lower ionisation potential energy and triplet excited state with a subsequent slightly higher adiabatic electron affinity value in comparison with [SP] AQ-PS-dG and AQ-PO-dG. Moreover, the energy gap between HOMO and LUMO, indicated the radical stabilisation properties of [RP] AQ-PS-dG, which can hinder the charge transfer through ds-DNA.

Structural, electronic and vibrational properties of GexCy (x+y=2–5) nanoclusters: A B3LYP-DFT study

An ab-initio study of the stability, structural and electronic properties has been made for 84 germanium carbide nanoclusters, GexCy (x+y=2–5). The configuration possessing the maximum value of final binding energy (FBE), among the various configurations corresponding to a fixed x+y=n value, is named as the most stable structure. The vibrational and optical properties have been investigated only for the most stable structures. A B3LYP-DFT/6-311G(3df) method has been employed to optimize fully the geometries of the nanoclusters. The binding energies (BE), highest-occupied and lowest-unoccupied molecular orbital (HOMO–LUMO) gaps have been obtained for all the clusters and the bond lengths have been reported for the most stable clusters. We have considered the zero point energy (ZPE) corrections. The adiabatic and vertical ionization potentials (IPs) and electron affinities (EAs), charge on atoms, dipole moments, vibrational frequencies, infrared intensities (IR Int.), relative infrared intensities (Rel. IR Int.) and Raman scattering activities have also been investigated for the most stable structures. The configurations containing the carbon atoms in majority are seen to be the most stable structures. The strong C–C bond has important role in stabilizing the clusters. For the clusters containing one germanium atom and all the other as carbon atoms, the BE increases monotonically with the number of the carbon atoms. The HOMO–LUMO gap, IPs and EAs fluctuates with increase in the number of atoms. The nanoclusters containing even number of carbon atoms have large HOMO–LUMO gaps and IPs, whereas the nanoclusters containing even number of carbon atoms have small EAs. In general, the adiabatic IP (EA) is smaller (greater) than the vertical IP (EA). The optical absorption spectrum or electron energy loss spectrum (EELS) is unique for every cluster, and may be used to characterize a specific cluster. All the predicted physical quantities are in good agreement with the experimental data wherever available. The growth of these most stable structures should be possible in the experiments.

Theoretical investigations of charge carrier transport in organic semiconductors of naphthalene bisimides N-substituted with alkoxyphenyl groups

Three novel alkoxyphenyl N-substituted naphthalene bisimide derivatives, N,N′-bis(4-n-butoxyphenyl)-1,8:4,5-naphthalenetetracarboxylic (NBI1), N,N′-bis(4-n-hexyloxyphenyl)-1,8:4,5-naphthalenetetracarboxylic (NBI2), and N,N′-bis(4-n-octyloxyphenyl)-1,8:4,5-naphthalenetetracarboxylic (NBI3) as potential organic semiconductors, have been investigated using density functional theory calculations coupled with the incoherent charge-hopping model at the molecular and crystal levels. The calculated results demonstrate that the low-lying and delocalized LUMOs and larger adiabatic electron affinities of these compounds are beneficial to their stability when acting as n-type organic semiconductors. The reorganization energy and transfer integral can significantly influence the charge carrier mobility. The compounds featured with the small reorganization energy and large transfer integral have relatively high charge mobilities. The electron coupling among the dominant hopping pathways indicates that the charge-transport processes happen in the parallel dimer of neighboring molecules with π–π interaction. The investigation of the angle dependence of charge carrier mobility showed that both NBI1 and NBI3 crystals exhibit remarkable anisotropic charge transporting behaviors. The calculated absorption spectra by the time-dependent density functional theory revealed that the strongest absorption peaks in the visible region are assigned to the π → π* transition and these peaks are regulated by the transitions of HOMO → LUMO. The calculated electron mobilities of NBI1, NBI2, and NBI3 are 0.0365, 0.0312, and 0.0801 cm2 V–1 s–1, respectively, indicating that these compounds are suitable for n-type organic semiconductors.

Spectroscopy of Ethylenedione.

The long sought-after, intrinsically short-lived molecule ethylenedione (OCCO) was observed and investigated by anion photoelectron spectroscopy. The adiabatic electron affinity of its quasi-bound (3)Σ(g)(-) state is 1.936(8) eV. The vibrational progression with a 417(15) cm(-1) frequency observed within the triplet band corresponds to a trans-bending mode. Several dissociative singlet states are also observed, corresponding to two components of the (1)Δg state and the (1)Σ(g)(+) state. The experimental results are in agreement with theoretical predictions and constitute the first spectroscopic observation and characterization of this elusive compound.

Spectroscopy of Ethylenedione

AbstractThe long sought‐after, intrinsically short‐lived molecule ethylenedione (OCCO) was observed and investigated by anion photoelectron spectroscopy. The adiabatic electron affinity of its quasi‐bound 3Σg− state is 1.936(8) eV. The vibrational progression with a 417(15) cm−1 frequency observed within the triplet band corresponds to a trans‐bending mode. Several dissociative singlet states are also observed, corresponding to two components of the 1Δg state and the 1Σg+ state. The experimental results are in agreement with theoretical predictions and constitute the first spectroscopic observation and characterization of this elusive compound.

Europium-doped silicon clusters EuSi n (n = 3–11) and their anions: structures, thermochemistry, electron affinities, and magnetic moments

The structures, electron affinities, and dissociation energies of EuSi n (n = 3–11) and their anions have been examined by means of four hybrid and pure density functional theory (DFT) methods. Basis sets used in this work are of segmented (SEG) Gaussian valence basis sets and relativistic small-core effective core potentials (ECP) with additional diffuse 2pdfg functions, denoted aug-SEG/ECP for Eu atoms and aug-cc-pVTZ for Si atoms. The geometries are fully optimized with each DFT method independently. The ground-state structures for all of these species are found to be substitutional type, which can be regarded as being derived from the ground-state structure of Si n+1 (and/or Si +1 − ) by replacing a Si atom with a Eu atom. The theoretical adiabatic electron affinities (AEAs) of EuSi n predicted by the four DFT schemes are in excellent agreement with the experimental data, especially the AEAs of TPSSh and B2PLYP. The average absolute deviations from experiment are by 0.10, 0.06, 0.07, and 0.05 eV, and the largest deviations are 0.16, 0.12, 0.18, and 0.10 eV at the B3LYP, TPSSh, PBE, and B2PLYP levels, respectively. The AEA of EuSi n (n = 3–11) is less than that of Si n . With the increase in silicon cluster size, the AEA of EuSi n may be close to that of Si n , but cannot be larger than that of Si n . The Eu atom acts as an electron donor, and the bonding between Eu and silicon clusters is ionic in nature. The bond between Eu and silicon clusters of neutral EuSi n (n = 3–11) is stronger than that of the anions. The total magnetic moments of EuSi n /EuSi (n = 3–11) and the magnetic moments on the Eu atom do not quench, and the total magnetic moments are contributed by Eu atom. The dissociation energies of Eu atom from EuSi n and their anions have also been calculated to examine relative stabilities.