Electron Detachment Energies Research Articles

First Evidence of Rhombic (NaCl)2-. Ab Initio Reexamination of the Sodium Chloride Dimer Anion

The possibility of electron binding to sodium chloride dimers in the gas-phase was studied at the coupled cluster level with single, double, and noniterative triple excitations using aug-cc-pVDZ+6s6p4d basis sets. It was found that three kinds of anions can be formedquasi-linear dipole-bound, nearly rhombic quadrupole-bound, and linear solvated-electron anions. In contrast to the earlier results, it was found that the rhombic neutral dimer (which is the neutral global minimum) does bind an excess electron to form an electronically stable anion of quadrupole nature. The global minimum on the ground-state anionic potential energy surface corresponds to the dipole-bound anion of quasi-linear structure (NaCl···NaCl)- whose vertical electron binding energy is 12 051 cm-1. It was also found that solvated-electron structure (ClNa···NaCl)- is considerably higher in energy than the anionic global minimum but its vertical electron detachment energy is significantly larger (i.e., 21 306 cm-1). The nearly rhombic (Na...

Discovery of a new class of stable gas-phase dianions: Mixed oxygen–carbon cluster OCn2− (n=5–19)

Small doubly charged negative cluster ions OCn2− were studied both by experimental and by theoretical means. In the experiments these dianions (with n=5–19) were produced by sputtering of a graphite specimen with a 14.5 keV Cs+ ion beam at an elevated oxygen partial pressure in the vicinity of the sample’s surface. The dianions and the corresponding singly charged OCn− (n⩽21) ions as well as homonuclear carbon dianions Cn2− were detected in a double-focusing mass spectrometer. The yields of the doubly and singly charged mixed oxygen-carbon ions increase with the ratio of the O2 arrival rate to the Cs+ flux density. The abundance distribution of OCn2− exhibits distinct even–odd alternations with the number of C atoms in the molecule. The flight time through the mass spectrometer of ∼15–25 μs establishes a lower limit with respect to the intrinsic lifetimes of the doubly charged ions. The theoretical studies investigated OCn2− dianions with n=5–8; the geometries of these species were optimized and the electronic stability was examined by the calculation of the electron detachment energies. In agreement with the low yield observed experimentally, OC52− is found to be weakly stable, whereas OC62−, OC72−, and OC82− are electronically stable gas-phase ions. In particular the latter is characterized by a large number of stable isomers.

Energetics of the Radical Ions of the AT and AU Base Pairs: A Density Functional Theory (DFT) Study

In this work, we present DFT calculations of the energetics of the base-pair anion and cation radicals of adenine−thymine (AT) and adenine−uracil (AU). At the B3LYP/6-31+G(d) level, we find that the adiabatic electron affinities (AEAs) are 0.30 eV for AT and 0.32 eV for AU. These values are both positive but slightly smaller than previously reported values for the AEA of guanine−cytosine (GC) and the hypoxanthine−cytosine base pair (IC). Furthermore, the AT and AU anion radical vertical electron detachment energies are also smaller than those of GC and IC, with that of AT only about half of GC's. For electron transfer between two identical isolated base pairs, the reorganization energies, λ, are calculated to be AT(0.76), AU(1.06), IC(1.25), and GC(1.31 eV). These results indicate that the AT base pair has a shallow trap depth and provides a favorable route for electron transfer, which explains previous experimental results that electron-transfer rates were higher in polydAdT than in polydGdC. Values of t...

A double Rydberg anion with a hydrogen bond and a solvated double Rydberg anion: Interpretation of the photoelectron spectrum of N2H7−

A double Rydberg anion has two electrons in diffuse orbitals that are bound by a closed-shell, cationic core. Low-energy features in the recently reported photoelectron spectrum of N2H7− are assigned to double Rydberg anions on the basis of electron propagator calculations employing Brueckner doubles, coupled-cluster reference states. The lowest electron detachment energy, 0.415 eV, corresponds to an initial state consisting of a hydrogen-bridged N2H7+ core and two diffuse electrons. A feature at slightly higher energy, 0.578 eV, belongs to a complex that comprises a tetrahedral NH4− double Rydberg anion and an ammonia solvent molecule. The most intense peak in the photoelectron spectrum, which occurs at 1.460 eV, pertains to a complex with a hydride anion and two ammonia solvent molecules. Plots of Dyson orbitals associated with electron detachment energies facilitate qualitative interpretation of electronic structure in the anions and in the neutral final states. Vibrational structure associated with each of these features has been interpreted as well. Previous assignments of electron detachment energies to the hydride–ammonia and tetrahedral isomers of NH4− have been confirmed with the present methods. Vibrationally excited final states have been assigned for this spectrum also.

Dipole-bound anions supported by charge-transfer interaction: valence- and dipole-bound anionic states of H 3N→BF 3

The possibility of electron binding to H 3NBF 3 was studied at the coupled cluster level of theory with single, double and non-iterative triple excitations. The neutral complex involves a dative bond that is responsible for a significant polarization of this species and generates a large dipole moment (6.53 D). As a consequence, H 3NBF 3 supports an electronically stable dipole-bound anionic state whose vertical electron detachment energy was calculated to be 2039 cm −1. In addition, a potential energy surface scan of the (H 3NBH 3) − indicates (for large separations between NH 3 and BF 3) the existence of a stable valence anion in which the excess electron is localized on the BF 3 monomer. These two anionic states (i.e., dipole- and valence-bound) can co-exist in some regions of the potential energy surface, and the dipole-bound state is more stable at the equilibrium geometry of the complex, while the valence anion is lower in energy at larger monomer–monomer separation.

Nondipole bound anions: Be2− and Be3−

Electron affinities (EAs) of beryllium clusters are calculated up to the complete coupled-cluster single double triple (CCSDT) level using reasonably large basis sets with many diffuse functions. At all levels of theory, the obtained values for the adiabatic EA are large enough to be observed with standard photodetachment techniques. The vertical electron detachment energy is 0.341 eV for Be2− and is 1.470 eV for Be3− at the most precise CCSDT level. All studied beryllium anions are valence bound but the nature of binding is different in Be2− and the two Be3− isomers. The only factor of stabilization of the excess electron in Be2− is the relaxation energy. Be3−(D∞h) is stabilized by the relaxation energy and the Koopmans electrostatic and exchange energies; in Be3−(D3h), the main factors of stabilization are the correlation and relaxation energies. As was revealed in our study, in linear molecules the correlation contribution to the electron binding energy is negative, i.e., it decreases the EA.

An ab Initio and Density Functional Study of Al3As, Al3As-, AlAs3, and AlAs3-

The low-lying electronic states of Al3As, AlAs3, and the corresponding anions have been studied at the B3LYP and CCSD(T) levels using the 6-311+G(2df) one-particle basis set. The ground electronic states of Al3As- and Al3As have a cyclic planar C2v geometry. A 1A1-(C3v) state is located 0.2 eV above the 1A1-(C2v) ground state of Al3As. For AlAs3, a near degeneracy is found between the 1A1 (C2v) and the 1A‘ (Cs) lowest states while the anion, AlAs-, has a 2A‘ (Cs) ground state. The adiabatic electron affinities of Al3As and AlAs3 are calculated to be 1.8 and 1.9 eV, respectively. Electron detachment energies computed for the anions and the harmonic vibrational frequencies of both the anions and the neutral molecules are presented and discussed. It is anticipated that the computed data will aid future analysis and the interpretation of experimental photoelectron photodetachment spectra of these systems.

Structure, electronic properties, and vibrational spectra of the water octamer with an extra electron: Ab initio study

The structure of the electron–water octamer has been investigated for the first time, using ab initio calculations. The lowest-energy conformer and the next lowest energy conformer are predicted to be the major and minor isomers with small and large vertical electron detachment energies. The binding energies and vibrational spectra are investigated.

An ab initio study on BeX 3− superhalogen anions (X = F, Cl, Br)

The vertical electron detachment energies (VDE) of 10 BeX 3 − (X = F, Cl, Br) anions were calculated at the outer valence Green function (OVGF) level with the 6-311++G(3df) basis sets. The largest vertical electron binding energy was found for BeF 3 − system (7.63 eV). All negatively charged species possess the vertical electron detachment energies that are larger than 5.5 eV and thus may be termed superhalogen anions. The strong dependence of the VDE of the BeX 3 − species on the ligand–central atom (Be–X) distance and on the partial atomic charge localized on Be was observed and discussed, as well as the other factors that may influence the electronic stability of such anions. In addition, the usefulness of the various theoretical treatments for estimating the VDEs of superhalogen anions was tested and analyzed.

Aromatic Carboxylate Superhalogens and Multiply Charged Anions

Ab initio calculations employing electron propagator theory and many-body perturbation theory show that the benzoate anion is a superhalide with an electron detachment energy in excess of 4.4 eV. Final states associated with vertical electron detachment energies of the benzoate anion are reordered by correlation effects, and the holes associated with the lowest neutral states thereby have O-centered σ character instead of ring-centered π character. Geometry optimizations on the dianions produced by attaching two carboxylate groups to the benzene ring arrive at planar structures for the para and meta isomers, but in the ortho isomer, a C2 structure with twisted OCO groups is found. The most stable isomer is para, and the least stable is ortho. The lowest vertical detachment energies are at least 1.4 eV for the para and meta isomers, but the estimate for the ortho isomer is 0.8 eV. Corresponding Dyson orbitals exhibit ring-centered π character. Attempts to find bound trianions with three carboxylate groups failed. In fluorinated compounds, the carboxylate groups rotate so that they are perpendicular to the ring planes. These compounds possess higher electron binding energies. The associated Dyson orbitals are delocalized over the ring, F, and carboxylate regions, and antibonding phase relationships are obtained between ring π and substituent lobes.

Dipole-bound and dispersion-bound anions supported by the asymmetric tautomers of aminophosphine: H 3NPH and HNPH 3

The binding of an excess electron to the ylides H 3NPH and HNPH 3 was studied at the coupled cluster level of theory with single, double, and non-iterative triple excitations and with extended basis sets to accommodate the loosely bound excess electron. It was found that these asymmetric tautomers of aminophosphine bind an excess electron to form stable anions. The vertical electron detachment energies corresponding to the H 3NPH and HNPH 3 forms were calculated to be 1816 and 32 cm −1 , respectively. It was found that while the H 3NPH tautomer forms a typical dipole-bound anion, the electron binding energy for the HNPH 3 tautomer calculated at the electrostatic Koopmans' theorem level is cancelled when the correlation correction to the dipole moment of the neutral is taken into account at the MP2 level. Therefore, we consider the (HNPH 3) anion as dispersion-bound since its stability is caused only by additional electron correlation effects, which are dominated by dispersion interaction.

Hydrated electron: Nonempirical cluster approach

AbstractInterface water anions composed of several chainlike or cyclic fragments were simulated with a 6‐31++G** basis set at the unrestricted Hartree–Fock level with the second‐order Moeller–Plesset perturbation theory corrections taken into account. The estimated vertical electron detachment energies (VDEs) of (H2O) anions were approximated by a VDE‐n−1/3 dependence close to the experimental one. A hypothesis about the predominant formation of interface structures under conditions of molecular flows is put forward. The atomic population analysis, character of the highest occupied molecular orbital, and changes in the geometry of interface anions with an increase in their molecular size reveal the compact localization of the excess electron density in water clusters and allow evaluating the effective excess‐electron radius of condensed water as 2.5 Å, in good agreement with a similar empirical estimate. The scope of the data obtained shows the relatively low probability of the formation of octahedral hydration shells compared to the tetrahedral coordination of solvating water molecules. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002

Gas-phase ion/molecule reactions in octafluorocyclobutane

Ion/molecule reactions in octafluorocyclobutane (c-C4F8) were studied using a high-pressure mass spectrometer. The thermochemical stabilities of the cluster ions of halide ions (X−) with c-C4F8 were measured. While the F− ion forms a covalent bond with c-C4F8, the interaction between other halide ions with c-C4F8 is mainly electrostatic. Theoretical calculation revealed that the halide ions interact not with the lowest unoccupied molecular orbital but with the next lowest unoccupied molecular orbital of the c-C4F8 molecule in the most stable cluster ions X−(c-C4F8). The electron affinity of c-C4F8 was measured to be 24.2±2.3 kcal/mol (1.05±0.10 eV) by observing the equilibria for reaction of SF6−+c-C4F8=c-C4F8−+SF6. While the sound equilibrium for that reaction was established in the temperature region from ∼350 K down to the lowest temperature measured (∼150 K), that was not established in the higher temperature region above 350 K. This was attributed to the existence of an isomer for c-C4F8− whose electron detachment energy is smaller than 1.05±0.10 eV. By the measurement of thermochemical stabilities of [(O2)m(c-C4F8)n]− (m+n=1–3), the lower electron affinity of c-C4F8 was determined to be 12.0±1.2 kcal/mol (0.52±0.05 eV). The lower limit of the proton affinity of c-C4F8 was estimated to be 130 kcal/mol.

Gas-phase stability of derivatives of the closo-hexaborate dianion B(6)H(6)(2-).

B(6)H(6)(2-) does not represent a stable gas-phase dianion, but emits spontaneously one of its excess electrons in the gas phase. In this work we address the question whether small stable gas-phase dianions can be constructed from the parent B(6)H(6)(2-) dianion by substitution of the hydrogens with appropriate ligands. Various hexa-, tetra-, and disubstituted derivatives B(6)L(6)(2-), B(6)H(2)L(4)(2-), and B(6)H(4)L(2)(2-) (L = F, Cl, CN, NC, or BO) are investigated with ab initio methods in detail. Four stable hexasubstituted B(6)L(6)(2-) (L = Cl, CN, NC, or BO) and three stable B(6)H(2)L(4)(2-) (L = CN, NC, or BO) gas-phase dianions could be identified and predicted to be observable in the gas phase. The trends in the electron-detachment energies depending on various ligands are discussed and understood in the underlying electrostatic pattern and the electronegativities of the involved elements.

An excess electron bound to urea. III. The urea dimer as an electron trap

The possibility of electron binding to urea dimers in the gas-phase was studied at the coupled cluster level with single and double excitations using aug-cc-pVDZ+7s6p5d basis sets. It was found that two kinds of anions can be formed—dipole-bound anions and solvated-electron anions. The global minimum on the ground-state anionic potential energy surface corresponds to the dipole-bound anion whose adiabatic and vertical electron binding energies are 484 and 1443 cm−1, respectively. It was also found that solvated electron structures, which are locally geometrically stable yet thermodynamically unstable, are considerably higher in energy than dipole-bound anions. However, the vertical electron detachment energies of the latter are significantly larger (i.e., 1267, 4129, and 7540 cm−1, depending on whether two canonical, one canonical, and one zwitterionic, or two zwitterionic urea monomers are involved, respectively), so their presence in any experimental source should allow them to be identified.

Solvated electrons in very small clusters of polar molecules: (HF)(3)(-).

Photoelectron spectra of (HF)(3)(-) reveal coexistence of two anionic isomers with vertical electron detachment energies (VDE) of 0.24 and 0.43 eV. The results of electronic-structure calculations, performed at the coupled cluster level of theory with single, double, and noniterative triple excitations, suggest that the two isomers observed experimentally are an open, zigzag, dipole-bound anion and an asymmetric solvated electron, in which the dipole-bound anion of (HF)(2) is solvated by one HF monomer at the side of the excess electron. The theoretical VDE of 0.21 and 0.44 eV, respectively, are in excellent agreement with the experimental data.

Photodetachment of Hydrated Sulfate Doubly Charged Anions: SO42-(H2O)n (n = 4−40)†

We produced hydrated clusters of the sulfate dianion, SO42-(H2O)n (n = 4−40), using electrospray ionization and investigated their energetics and stabilities using photodetachment photoelectron spectroscopy (PES) at four photon energies. The adiabatic electron detachment energies of the hydrated cluster dianions were observed to increase with the number of water, from ∼0.4 eV for n = 3, the smallest number of water to stabilize SO42- in the gas phase, to ∼5.7 eV for n = 40. The PES features of the smaller clusters are similar, all due to the SO42- dianion, which was found to be in the center of the solvated clusters. The intensity of the SO42- solute PES features was observed to decrease with solvent coverage beyond the first solvation shell (n ≈ 12), whereas a strong high binding energy feature due to ionization of the solvent emerged. For n > 30, the solute PES features almost completely disappeared, and the water feature became dominant. The photon energy dependent studies allowed us to examine the rep...

Linking the photoelectron and infrared spectroscopies of the (H2O)6− isomers

We report a novel photoelectron spectroscopy variation of population labeling spectroscopy and apply it to assign the isomeric carrier of the strong autodetaching OH stretching vibrational resonances reported previously [J. Phys. Chem. 100, 16782 (1996) and J. Chem. Phys. 108, 444 (1998)] for a mixed ensemble of (H2O)6− isomers. The vibrational bands are traced to the isomer with the higher vertical electron detachment energy (VDE). This result indicates that resonances are most readily observed for vibrational bands which lie below the VDE of the parent species.

ｃ‐Ｃ４Ｆ８の関与する特異なイオン‐分子反応

Ion/molecule reactions in octafluorocyclobutane (c-C4F8) were studied using a high-pressure mass spectrometer. The thermochemical stabilities of the cluster ions of halide ions (X-) with c-C4F8 were measured. While the F- ion forms a covalent bond with c-C4F8, the interaction between other halide ions with c-C4F8 is mainly electrostatic. Theoretical calculation revealed that the halide ions interact not with the lowest unoccupied molecular orbital but with the next lowest unoccupied molecular orbital of the c-C4F8 molecule in the most stable cluster ions X- (c-C4F8). The electron affinity of c-C4F8 was measured to be 24.2±2.3 kcal/mol (1.05±0.10 eV) by observing the equilibria for reaction of SF6-+c-C4F8 = c-C4F8-+SF6- While the sound equilibrium for that reaction was established in the temperature region from ∼350 K down to the lowest temperature measured (∼150 K), that was not established in the higher temperature region above 350 K. This was attributed to the existence of an isomer for c-C4F8- whose electron detachment energy is smaller than 1.05 ev. By the measurement of thermochemical stabilitries of [(O2)m(c-C4F8)n]- (m+n = 1-3), the lower electron affinity of c-C4F8 was determined to be 12.0±1.2 kcal/mol (0.52±0.05 eV). The lower limit of the proton affinity of c-C4F8 was estimated to be 130 kcal/mol.

Electron binding energies of nucleobases and nucleotides

AbstractElectron propagator theory is applied to the calculation and interpretation of electron binding energies of molecular fragments found in nucleic acids. This theory provides a systematic approach to correlation problems in quantum chemistry while retaining a one‐electron picture of electronic structure. Photoelectron spectra for the purine and pyrimidine bases found in nucleic acids have been assigned with the aid of calculations that employ an electron propagator approximation that has been developed for the study of large molecules. This method, the partial third‐order approximation (P3), has been shown to generate reliable electron binding energies for closed‐shell molecules and anions. Correlation corrections to canonical, Hartree–Fock orbital energies are necessary for assignment of cationic states. Electron detachment energies for H2PO also have been assigned successfully with the P3 method. These results indicate that the P3 method is a suitable procedure for predicting electron binding energies of nucleotide anions. Correlation effects are important in determining the ordering of final states with holes localized on the phosphate or the base regions in the nucleotide. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002