Piotr Skurski

Energies of dipole-bound anionic states

Dipole-bound anionic states of CH CN, C H , and HF were studied using highly 33 2 2 correlated electronic structure methods and extended one-electron basis sets. The electron detachment energies were calculated using the coupled cluster method with single, double, and noniterative triple excitations. Geometrical relaxation of the molecular framework upon electron attachment and the difference in the harmonic zero-point vibrational energies between the neutral and the dipole-bound anionic species were calculated at the MP2 level of theory. We demonstrate that the dispersion interaction between the loosely bound electron and the electrons of the neutral molecule is an important component of the electron binding energy, comparable in magnitude to the electrostatic electron)dipole stabilization. The geometrical relaxation upon electron attachment and the change in the zero-point vibrational energy is important for the weakly bound HF dimer. The predicted values of the vertical electron detachment energies for the dipole bound states of CH CN and C H of 112 and 188 cm y1 , 33 2 respectively, are in excellent agreement with the recent experimental results of 93 and y1 . y

BX4- and AlX4- superhalogen anions (X = F, Cl, Br): an ab initio study.

The vertical electron detachment energies (VDEs) of 30 MX 4 (-) (M = B, Al; X = F, Cl, Br) anions were calculated at the OVGF level with the 6-311+G(3df) basis sets. The largest vertical electron binding energy was found for the AlF 4 (-) system (9.789 eV). The strong VDE dependence on the symmetry of the species, ligand type, ligand-central atom distance, and bonding/nonbonding/antibonding character of the highest occupied molecular orbital was observed and discussed.

Halogenoids as Ligands in Superhalogen Anions

The superhalogen compounds are of great importance in chemistry due to their enormously high electron affinities (approaching 13 eV). The utilizing halogenoids as ligands in the superhalogen anionic species is proposed and discussed on the basis of the ab initio outer valence Green function (OVGF) theoretical results. The representative species, such as LiX(2)(-), NaX(2)(-), BeX(3)(-), MgX(3)(-), CaX(3)(-), BX(4)(-), and AlX(4)(-) (where X stands for a halogenoid group), were designed and studied at the OVGF/6-311+G(3df)//MP2/6-311+G(d) level. It was found that the halogenoids (CN, NC, OCN, NCO, SCN, and NCS) might be used as ligands while designing novel superhalogen anions. The lowest and highest electron binding energies for the species considered were found for the Na(NCS)(2)(-) (5.010 eV) and Al(NC)(4)(-) (9.209 eV), respectively. The desired range of the electronic stability of the resulting species might be achieved by the proper choice of the central metal atom and the halogenoid ligand.

Moderately Reactive Molecules Forming Stable Ionic Compounds with Superhalogens

An explanation of the ability of selected moderately reactive molecules to form stable systems with superhalogens (AlF(4) and AlCl(4)) is provided on the basis of theoretical considerations supported by ab initio calculations. It is demonstrated that even the molecules possessing high ionization potentials (such as SiO(2), NH(3), CHCl(3), CCl(2)F(2)) should form stable and strongly bound ionic compounds when combined with a properly chosen superhalogen system (acting as an oxidizing agent). The conclusion is supported by providing the structural parameters and interaction energies for the SiO(2)AlF(4), NH(3)AlF(4), CHCl(3)AlF(4), CCl(2)F(2)AlF(4), SiO(2)AlCl(4), and NH(3)AlCl(4) compounds obtained at the CCSD(T)/6-311++G(d,p)//MP2/6-311++G(d,p) level. On the other hand, the AlF(4) and AlCl(4) superhalogens were found to be incapable of reacting with molecules whose ionization potentials (IP) exceed 13 eV (e.g., CO(2), CH(4)). Finally, it is demonstrated that the competition between the electron binding energy of the superhalogen system and the IP of the molecule the superhalogen is combined with is a key factor for predicting the stability of certain species.

An ab initio study of the betaine anion–dipole-bound anionic state of a model zwitterion system

The electron binding to a model zwitterionic molecule, betaine, is studied at the coupled cluster level of theory with single, double, and noniterative triple excitations as well as at the density functional theory level. Our results indicate that there is only one stable conformer of betaine with a dipole moment of 11.5 D. This dipole moment supports a relatively strongly bound anionic state and the vertical electron detachment energy was found to be 2261 cm−1. Furthermore, we predict the excess electron binding energy for the betaine analog with a blocked canonical structure (N,N-dimethylglycine methyl ester) to be less than 100 cm−1. This significant difference in electron binding energies suggests that the gas phase instability of zwitterions of some common naturally occurring amino acids with respect to their canonical forms may be reversed by the excess electron attachment. The calculated Franck–Condon factors for the betaine’s anion/neutral pair suggest that the photoelectron spectrum of the anion ...

Theoretical Search for Alternative Nine-Electron Ligands Suitable for Superhalogen Anions

The calculations performed at the OVGF/6-311++G(3df,3pd)//MP2/6-311++G(d,p) level for the representative NaX(2)(-) and AlX(4)(-) anions matching the MX(k+1)(-) superhalogen formula and utilizing 9-electron systems (i.e., consisting of various possible combinations of atoms containing nine electrons when brought together) revealed that the OH, Li(2)H(3), and NH(2) groups might be considered as alternative ligands X due to their thermodynamic stability and large values of electron binding energy (approaching or even exceeding 6 eV in some cases). All aluminum-containing AlX(4)(-) anions (excluding Al(HBLi)(4)(-)) were predicted to be thermodynamically stable, whereas the NaX(2)(-) anions for X = CH(3), HBLi, CLi, BeB, and H(2)BeLi were found to be susceptible to the fragmentations leading to Na(-) loss. Among the MX(k+1)(-) (M = Na, Al; X = Li(2)H(3), OH, H(2)BeLi, BeB, NH(2), HBLi, CH(3), Be(2)H, CLi) anions utilizing systems containing 9 electrons (and thus isoelectronic with the F atom) the largest vertical electron detachment energy of 6.38 eV was obtained for Al(OH)(4)(-).

Strength of the Lewis-Brønsted Superacids Containing In, Sn, and Sb and the Electron Binding Energies of Their Corresponding Superhalogen Anions.

The HInnF3n+1, HSnnF4n+1, and HSbnF5n+1 (n = 1-3) compounds and their corresponding InnF3n+1(-), SnnF4n+1(-), SbnF5n+1(-) (n = 1-3) anions were investigated by employing the B3LYP, QCISD, and OVGF quantum chemistry methods and the LANL2DZ/6-311++G(d,p) basis sets. Our calculations revealed very strong acidity of all examined neutral compounds and large electronic stabilities (in the range 9.9-13.3 eV) of their corresponding anions. The gas phase acidities (manifested by small Gibbs free energies of deprotonation, ΔGacid) predicted for the HSn3F13 and HSb3F16 (ΔGacid of 243.5 and 230.3 kcal/mol at T = 298.15 K, respectively) suggest that these systems should actually act as even stronger acids than the F(SO3)4H and HSbF6 compounds (recognized thus far as the strongest superacids).

The origin of luminescence accompanying electrochemical reduction or chemical decomposition of peroxydisulfates

Abstract The spectral features of the electrochemiluminescence occurring during the reduction of peroxydisulfate anions at magnesium, silver or platinum electrodes (ecl), the luminescence following their decomposition on a magnesium surface (mcl), and the chemiluminescence accompanying the thermal decomposition of peroxydisulfates in acidic media (tcl), were thoroughly examined in order to discover the origin of the light emission. The intensity of emission followed the order ecl>mcl⪢tcl and depended on the method of its generation and other experimental conditions. Probable pathways of the reactions leading to the formation of light-emitting species were examined at the density functional theory level. The theoretical studies and experimental findings seem to indicate that the luminescence originates from 1 O 2 , 1 (O 2 ) 2 and 3 (O 2 ) 2 , the precursors of which are SO 4 •− , HO • , HOO • , HOOH and O 3 formed in the primary and secondary processes following electrochemical reduction or thermal decomposition of peroxydisulfates. Supplementary experiments demonstrated the participation of HOOH in the generation of light emitting entities.

The Reason Why HAlCl4 Acid Does Not Exist

The explanation of the hypothetical HAlCl(4) acid instability is provided on the basis of theoretical considerations supported by ab initio calculations. The equilibrium structures of LiAlCl(4), NaAlCl(4), and KAlCl(4) salts were examined and compared to that of their corresponding parent acid. The process of formation of the representative NaAlCl(4) salt was analyzed, and the interaction energy between NaCl and AlCl(3) was estimated to be ca. 55 kcal/mol while that between HCl and AlCl(3) (when the HAlCl(4) species is formed) was calculated to be smaller by an order of magnitude (ca. 8 kcal/mol). The hypothetical HAlCl(4) acid was identified as an HCl...AlCl(3) adduct (with the hydrogen chloride tethered weakly to the quasi-planar aluminum chloride molecule). The electron affinity of the neutral AlCl(4) superhalogen molecule was found to be the factor determining the ability to form a stable compound of MAlCl(4) type.

Electron binding energies in linear dipole-bound (HCN)n− (n=2–5) anions

Abstract The (HCN) 2 − anion has been studied at the coupled cluster level of theory with single, double, and non-iterative triple excitations whereas equilibrium structures and electron binding energies for larger linear (HCN) n − ( n =3–5) clusters have been determined at the second-order Moller–Plesset (MP2) level. The adiabatic electron affinity of (HCN) 2 was found to be 399 cm −1 and trends in physically meaningful components of electron binding energy, such as static Coulomb, dispersion, and polarization stabilizations, were determined for this series of clusters. The 2 Π dipole-bound anionic state was found for the pentamer with the MP2 vertical electron detachment energy of 92 cm −1 .