Valence Electron Affinity Research Articles

The valence electron affinity of uracil determined by anion cluster photoelectron spectroscopy.

The unoccupied π* orbitals of the nucleobases are considered to play important roles in low-energy electron attachment to DNA, inducing damage. While the lowest anionic valence state is vertically unbound in all neutral nucleobases, it remains unclear even for the simplest nucleobase, uracil (U), whether its valence anion (U-) is adiabatically bound, which has important implications on the efficacy of damage processes. Using anion photoelectron spectroscopy, we demonstrate that the valence electron affinity (EAV) of U can be accurately measured within weakly solvating clusters, U-(Ar)n and U-(N2)n. Through extrapolation to the isolated U limit, we show that EAV = -2 ± 18 meV. We discuss these findings in the context of electron attachment to U and its reorganization energy, and more generally establish guidance for the determination of molecular electron affinities from the photoelectron spectroscopy of anion clusters.

Hyperfine electron affinities of molecular oxygen

Theoretical hyperfine valence electron affinities of O2 are identified in thermal, electron impact, photon and electrochemical data. The ranges of the 162 values are: (eV) 72-[X2Π, 1.030(2) to 1.100(2): C2Π, 0.410(2) to 0.480(2); d4Π, 0.228 to 0.342; f4Π, 0.128 to 0.242]; 36-[b4Δ, 0.685 to 0.917; A2Δ, 0.541 to 0.611]; 54-[a4Σ, 0.920 to 0.990; e4Σ, 0.215 to 0.285; b4Σ, 0.710 to 0.780; B2Σ, 0.495 to 0.545; D2Σ, 0.395 to 0.445; E2Σ, 0.335 to 0.385]. These demonstrate the existence of 162 bonding and 162 antibonding hyperfine states dissociating to the lowest limits. Multiple long range Efimov-like states with electron affinities less than 0.10eV are also identified.

On the Electron Affinity of Nitromethane (CH3NO2)

A high-level systematic computational study is presented on an accurate value for the adiabatic valence electron affinity of nitromethane, CH(3)NO(2), to resolve literature disagreements in theoretical and experimental reported values. Density functional methods with triple-zeta quality basis sets gave good fortuitous agreement to early experimental determinations, while single-reference wave function based methods employing up to CCSD(T) gave poor or fortuitous agreement depending on the experimental reference value. DFT methods in general cannot accurately describe electron attachment from the result of unphysical self-interaction. It is found that multireference methods with aug-cc-pVTZ or similar basis sets are required to converge to an experimental value. Our highest level of theory 3S-MCQDPT2 and 7S-MCQDPT2 calculations with an aug-cc-pVTZ quality basis description yield values of 0.188 and 0.176 eV (0.170 eV with polynomial extrapolation), in excellent agreement with the most recent experimental value of 0.172 +/- 0.006 eV. CCSD(T)//aug-cc-pVTZ provides a fortuitously reasonable description. The isolated dipole-bound anion binding energy is tentatively calculated to be 7-8 meV.

The density functional theory study on the ionization potentials and electron affinities of cytosine-formamide complexes

Accurate adiabatic and vertical ionization potentials (IPs) and valence electron affinity (EA) of cytosine and cytosine-formamide complexes have been determined using density functional theory B3LYP. Comparison has been made with the data from a recently published study, as well as earlier studies on cytosine. For cytosine-formamide complexes it is found that the hydrogen bond interactions between cytosine and formamide play a more important role in the process of electron attachment than in the process of electron detachment. Meanwhile, the hydrogen bond interactions facilitate the adiabatic electron detachment and attachment but have different effects on the vertical electron detachment and attachment with different positions of formamide.

In search for an optimal methodology to calculate the valence electron affinities of temporary anions

Recently, we have proposed an approach for finding the valence anion ground state, based on the stabilization exerted by a polar solvent; the methodology used standard DFT methods and relatively inexpensive basis sets and yielded correct electron affinity (EA) values by gradually decreasing the dielectric constant of the medium. In order to address the overall performance of the new methodology, to find the best conditions for stabilizing the valence state and to evaluate its scope and limitations, we gathered a pool of 60 molecules, 25 of them bearing the conventional valence state as the ground anion and 35 for which the lowest anion state found holds the extra electron in a diffuse orbital around the molecule (non valence state). The results obtained by testing this representative set suggest a very good performance for most species having an experimental EA less negative than -3.0 eV; the correlation at the B3LYP/6-311+G(2df,p) level being y = 1.01x + 0.06, with a correlation index of 0.985. As an alternative, the time dependent DFT (TD-DFT) approach was also tested with both B3LYP and PBE0 functionals. The methodology we proposed shows a comparable or better accuracy with respect to TD-DFT, although the TD-DFT approach with the PBE0 functional is suggested as a suitable estimate for species with the most negative EAs (ca.-2.5 to -3.5 eV), for which stabilization strategies can hardly reach the valence state. As an application, a pool of 8 compounds of key biological interest with EAs which remain unknown or unclear were predicted using the new methodology.

DFT calculations of the ionization potentials and electron affinities of serinamide

AbstractAdiabatic and vertical ionization potentials (IPs) and valence electron affinities (EAs) of serinamide in the gas phase have been determined using density functional theory (DFT) B3LYP, B3P86, and B3PW91 methods with the 6‐311++G** and 6‐311G** basis sets, respectively. IPs and EAs of serinamide in solution have been calculated with the B3LYP method using the 6‐311++G** and 6‐311G** basis sets. Eight possible conformers of serinamide and its charged states in the gas phase have been optimized employing the DFT B3LYP method with 6‐311++G** and 6‐311G** basis sets, respectively. All the adiabatic and vertical ionization potentials (AIPs and VIPs) of eight serinamide conformers in our work are positive values, whether in the gas phase or in solutions; the IPs in solutions are smaller than the results in the gas phase and decrease with increased dielectric constants in solutions. This finding indicates that the cationic states in solutions are more stable than those in the gas phase. All EAs of eight serinamide conformers are negative values in the gas phase, indicating that the anionic states are unstable with respect to electron autodetachment, both adiabatically and vertically. In contrast, all other adiabatic electron affinities (AEAs) are negative values in solutions except for 6S in water; 7S in chloroform, acetone, and water; and 8S in acetone and water, and increase with increasing of dielectric constants in solutions. All vertical electron affinities (VEAs) are negative values in solutions; however, no good rule has been found for these values in solutions. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006

Electron attachment to strongly polar clusters

Electron localization is studied in formamide cluster anions. The isolated formamide molecule has a large dipole moment and its clusters can give birth to multipole-bound anions as well as valence anions. The vertical valence electron affinity of the isolated molecule is determined by electron transmission spectroscopy. The anion formation process is studied as a function of cluster size with Rydberg electron transfer spectroscopy. DFT calculations of the neutral and negatively-charged cluster structures show that the anion excess electron localizes on a single molecule. The adiabatic valence electron affinity of isolated formamide is deduced from the observation of the cluster size threshold for valence attachment.

Theoretical Determinations of Ionization Potential and Electron Affinity of Glycinamide Using Density Functional Theory

Accurate vertical (adiabatic) ionization potential (IP) and valence electron affinity (EA) of glycinamide, including its possible conformers, have been determined employing density functional theory (B3LYP) with 6-311++G** and 6-311G** basis sets, respectively. The calculated adiabatic IPs are 8.60, 8.57, 8.52, and 8.49 eV for conformer IA, IIA, IIIA, and IV, respectively, decreasing gradually with the decreasing of their relative stabilities. Comparisons with glycine indicate that the substitute of −NH2 for −OH in glycine decreases its ionization potential. In various solutions, IPs decrease apparently with respect to those in the gas phase. All electron affinities of glycinamide conformers are negative values in the gas phase, indicating that the anionic states are unstable with respect to electron autodetachment vertically and adiabatically. On the contrary, all of the adiabatic EAs in solution possess positive values and become larger and larger with the increasing of dielectric constants. Additionall...

DFT Calculations of the Electron Affinities of Nucleic Acid Bases: Dealing with Negative Electron Affinities

To better understand the cause of the diversity in reported values of the electron affinities (EAs) for DNA bases, we performed a series of DFT (B3LYP functional) calculations at different basis set sizes. Through investigation of (1) trends in the values of EAs, (2) the excess electron spin distribution of the anion radical dependence on basis set size, (3) effect of the excess electron on ZPEs, we are able to identify the features of a basis set that allows for dipole-bound and continuum states to compete with molecular states for the electron. Smaller basis sets that confine the excess electron to the molecule allow for reasonable estimates of relative valence electron affinities excluding dipole-bound states and suggest the order of adiabatic valence electron affinities to be U ≈ T > C ≈ I (hypoxanthine) > A > G with G nearly 1 eV less electron affinic than U. Combining the best estimates from theory and experiment we place the adiabatic valence electron affinities of the pyrimidines as zero to +0.2 e...

Structures and electron affinities of indole–(water)N clusters

Rydberg electron transfer spectroscopy (RET) has been used to determine the dipole-bound electron affinity of the indole molecule, and the value of 3 meV was obtained. RET has also been employed to study [indole–(water)N]− cluster anions and the results have been interpreted with the help of ab initio calculations. It has been shown that for N=1 and 2 only dipole-bound anions are formed and that the electron attachment induces large amplitude motions in these systems. [Indole–(water)N]− anions with N=3 and 4 have not been observed. This finding for N=3 is consistent with a low theoretically predicted dipole moment of the neutral indole–(water)3 complex, which is insufficient for the formation of a stable dipole-bound anion. Above N=5, RET experiments showed formation of valence [indole–(water)N]− anions. From the observed size threshold for the formation of these anions, the negative value of the valence electron affinity of indole equal to −1.03±0.05 meV was deduced.