Gennady L. Gutsev

Origin of the unusual stability of MnO4

Abstract The attachment of an electron to manganese tetroxide cluster is found to lower its total energy by as much as 5 eV, thus putting MnO 4 into the class of superhalogens. This result, predicted by first-principles calculations based on density functional theory and generalized gradient approximation, is verified experimentally by photodetachment spectroscopy. The combined theoretical and experimental studies not only allow a fundamental understanding of the origin of the unusual stability of MnO 4 − but also provide information on ground-state geometries, vibrational frequencies, and electronic structure of MnO 4 , MnO 4 − , and their isomers.

Adiabatic electron affinities of small superhalogens: LiF2, LiCl2, NaF2, and NaCl2

Geometries and frequencies for the neutral MX2 and ionic MX2− species (M=Li, Na, and X=F, Cl) are studied by several theoretical methods: density functional theory (Becke-3-Lee-Yang-Parr) [DFT(B3LYP)], second-order many-body perturbation theory [MBPT(2)], and coupled-cluster with singles and doubles (CCSD). The geometries optimized at the CCSD/6-311+G(d) level are used in CCSD(T) calculations with a large atomic natural orbital basis to compute adiabatic electron affinities (EAad), which are found for LiF2, LiCl2, NaF2, and NaCl2 to be 5.45, 4.97, 5.12, and 4.69 eV, respectively. The highest EAs among all the atoms of the periodic table occur in the halogen atoms (fluorine, 3.40 eV; chlorine, 3.62 eV); therefore all four of these triatomic radicals are properly termed superhalogens. LiF2, LiCl2, NaF2, and NaCl2 are thermodynamically stable, and their dissociation energies computed at the CCSD with the noniterative inclusion of triples [CCSD(T)] level are 20.5, 24.9, 19.3, and 25.2 kcal/mol, respectively. ...

Electron affinities of CO2, OCS, and CS2

The structure of the CO2−, OCS−, and CS2− anions as well as the adiabatic electron affinities of the corresponding CO2, OCS, and CS2 neutral parents are computed using the infinite-order coupled-cluster method with all singles and doubles and non-iterative inclusion of triple excitations (CCSD(T)) and Hartree-Fock-Density-Functional-Theory (HFDFT) levels of theory. The potential energy curves of the CO2 – CO2− and CS2 – CS2− pairs are calculated as a function of the bending angle. All three anions are found to have bent equilibrium configurations. The adiabatic electron affinities of CO2 and OCS are calculated to be negative, whereas the CS2− anion is stable in the linear and relaxed geometries. The existence of CS2− at linear geometries can be related to experimental observations of an electric field-induced detachment of an extra electron from the anion in fields of only a few kilovolts per centimeter.

A THEORETICAL STUDY OF THE VALENCE- AND DIPOLE-BOUND STATES OF THE NITROMETHANE ANION

The valence‐ and dipole‐bound states of CH3NO−2 are studied at the CCSD(T), HFDFT (B3LYP), and EA‐EOMCC levels of theory. At both CCSD(T) and HFDFT levels, we have found a positive valence EA in nice agreement with the experimental data. The binding energy of the dipole‐bound electron is about 13 meV according to the EA‐EOMCC calculations. Interaction of the valence‐ and dipole‐bound states (DBS) of CH3NO−2 is complicated, since the dipole‐bound state exists at the equilibrium geometry of the anion and corresponds to an excited state of the valence‐bound anion. Hence, excitations of the valence anionic state could lead to both the detachment of an electron or formation of a DBS, whose geometry is similar to the geometry of the neutral parent. At the equilibrium geometry of the anion, the energies of the dipole‐bound and valence states are close to each other. Since typical lifetimes of rovibrational excited states of a DBS are two orders of magnitude higher than the lifetimes of ordinary vibrationally exc...

Electronic structure of chromium oxides, CrOn− and CrOn(n=1–5) from photoelectron spectroscopy and density functional theory calculations

The electronic structure of CrOn− and CrOn (n=1–5) was investigated using anion photoelectron spectroscopy and density functional theory. Photoelectron spectra of CrOn− were obtained at several photon energies and yielded electron affinities, vibrational and electronic structure information about the neutral CrOn species. Density functional theory calculations were carried out for both the neutrals and anions and were used to interpret the experimental spectra. Several low-lying electronic states of CrO were observed and assigned from photodetachment of the CrO− ground state (6∑+) and an excited state (4∏), which is only 0.1 eV higher. The main spectral features of CrO2− were interpreted based on a C2v CrO2− (4B1). A very weak Cr(O2)− isomer was also observed with lower electron binding energies. Relatively simple and vibrationally resolved spectra were observed for CrO3−, which was determined to be D3h. The CrO3 neutral was calculated to be C3v with the Cr atom slightly out of the plane of the three O at...

Structure and stability of BF3∗F and AlF3∗F superhalogens

Abstract Structure and stability of BF4, AlF4, BF4− and AlF4− are studied at the MBPT(4) and CCSD(T) levels of theory. AlF4 is confirmed to have a configuration of an adduct type, which is stable by 5.8 kcal/mol towards AlF3+F. BF4 has to be considered rather as a Van der Waals complex which is bound by 1.6 kcal/mol. BF3∗F and AlF3∗F possess very high adiabatic electron affinities of 6.75 and 7.93 eV, respectively, and are superhalogens. We computed the adiabatic electron affinities of BF3 and AlF3 to be −0.76 and 0.90 eV, respectively, which indicates that BF3− is metastable.

A systematic study of neutral and charged 3d-metal trioxides and tetraoxides

Using density functional theory with generalized gradient approximation, we have performed a systematic study of the structure and properties of neutral and charged trioxides (MO(3)) and tetraoxides (MO(4)) of the 3d-metal atoms. The results of our calculations revealed a number of interesting features when moving along the 3d-metal series. (1) Geometrical configurations of the lowest total energy states of neutral and charged trioxides and tetraoxides are composed of oxo and∕or peroxo groups, except for CuO(3)(-) and ZnO(3)(-) which possess a superoxo group, CuO(4)(+) and ZnO(4)(+) which possess two superoxo groups, and CuO(3)(+), ZnO(3)(+), and ZnO(4)(-) which possess an ozonide group. While peroxo groups are found in the early and late transition metals, all oxygen atoms bind chemically to the metal atom in the middle of the series. (2) Attachment or detachment of an electron to∕from an oxide often leads to a change in the geometry. In some cases, two dissociatively attached oxygen atoms combine and form a peroxo group or a peroxo group transforms into a superoxo group and vice versa. (3) The adiabatic electron affinity of as many as two trioxides (VO(3) and CoO(3)) and four tetraoxides (TiO(4), CrO(4), MnO(4), and FeO(4)) are larger than the electron affinity of halogen atoms. All these oxides are hence superhalogens although only VO(3) and MnO(4) satisfy the general superhalogen formula.

Structure and stability of the AlX and AlX− species

The electronic and geometrical structures of the ground and low-lying excited states of the diatomic AlX and AlX− series (X=H, Li, Be, B, C, N, O, and F) are calculated by the coupled-cluster method with all singles and doubles and noniterative inclusion of triples using a large atomic natural orbital basis. All the ground-state AlX molecules except for AlF can attach an additional electron and form ground-state AlX− anions. The ground-state AlBe−, AlB−, AlC−, AlN−, and AlO− anions possess excited states that are stable toward autodetachment of an extra electron; AlBe− also has a second excited state. Low-lying excited states of all AlX but AlN can attach an extra electron and form anionic states that are stable with respect to their neutral (excited) parent states. The ground-state AlLi−, AlBe−, AlB−, AlN−, and AlO− anions are found to be thermodynamically more stable than their neutral parents. The most stable is AlO−, whose dissociation energy to Al+O− is 6.4 eV. Correspondingly, AlO possesses the larg...

Structure and properties of the aluminum borates Al(BO2)n and Al(BO2)n−, (n = 1–4)

The geometrical and electronic structures of Al(BO2)n and Al(BO2)n− (n = 1–4) clusters are computed at different levels of theory including density functional theory (DFT), hybrid DFT, double‐hybrid DFT, and second‐order perturbation theory. All aluminum borates are found to be quite stable toward the BO2 and BO2− loss in the neutral and anion series, respectively. Al(BO2)4 belongs to the class of hyperhalogens composed of smaller superhalogens, and should possess a large adiabatic electron affinity (EAad) larger than that of its superhalogen building block BO2. Indeed, the aluminum tetraborate possesses the EAad of 5.6 eV, which, however, is smaller than the EAad of 7.8 eV of the AlF4 supehalogen despite BO2 is more electronegative than F. The EAad decrease in Al(BO2)4 is due to the higher thermodynamic stability of Al(BO2)4 compared to that of AlF4. Because of its high EA and thermodynamic stability, Al(BO2)4 should be capable of forming salts with electropositive counter ions. We optimized KAl(BO2)4 as corresponding to a unit cell of a hypothetical KAl(BO2)4 salt and found that specific energy and energy density of such a salt are competitive with those of trinitrotoluol (TNT).

Negative ions of transition metal-halogen clusters

A systematic density functional theory based study of the structure and spectroscopic properties of neutral and negatively charged MX(n) clusters formed by a transition metal atom M (M=Sc,Ti,V) and up to seven halogen atoms X (X=F,Cl,Br) has revealed a number of interesting features: (1) Halogen atoms are bound chemically to Sc, Ti, and V for n≤n(max), where the maximal valence n(max) equals to 3, 4, and 5 for Sc, Ti, and V, respectively. For n>n(max), two halogen atoms became dimerized in the neutral species, while dimerization begins at n=5, 6, and 7 for negatively charged clusters containing Sc, Ti, and V. (2) Magnetic moments of the transition metal atoms depend strongly on the number of halogen atoms in a cluster and the cluster charge. (3) The number of halogen atoms that can be attached to a metal atom exceeds the maximal formal valence of the metal atom. (4) The electron affinities of the neutral clusters abruptly rise at n=n(max), reaching values as high as 7 eV. The corresponding anions could be used in the synthesis of new salts, once appropriate counterions are identified.