Hydration of the ions Al3+ and Cu2+. An ab initio SCF study

Ab initio calculations are reported for the systems Al(H₂O)_n³⁺ and Cu(H₂O)_n²⁺ with n up to 7. The calculated binding energies increase monotically up to n = 6, with equal binding energies for n = 6 and 7 for the Al³⁺ cation. An estimate of the enthalpy of hydration of Al³⁺ is given, based on model calculations with one or two water molecules from the second solvation shell. An SN1 (dissociative) mechanism for the exchange of the water molecules from the first hydration shell of Al³⁺ appears energetically favorable if the leaving molecule remains in the second hydration shell.     

Excited states of gaseous ions. IV. Potential energy surfaces of the H2O+ ion

Cross-sections of the potential energy hypersurfaces are reported for the four lower-lying states of the H₂O⁺ molecular ion. The symmetric dissociation of the ion has been investigated using the CNDO/2 method supplemented by a configuration interaction calculation. Self-consistent-field wave functions were calculated for the asymmetric dissociation using an extended basis of Gaussian-lobe functions. The values of the hydrogen exponents are found to be very sensitive to the molecular geometry. The calculated equilibrium H-O-H angle is 123° in the X?²B₁ state, nearly 180° in the X?A²A₁ state and 69° in the B?²B₂ state. The lower-lying quartet á ⁴B₁ is line entirely repulsive. The potential energy surface of the à ²A₁ state has a peculiar shape, characterized by two dissociation valleys.     

An ab initio potential energy surface for the reaction N+ + H2 → NH+ + H

Preliminary results of ab initio unrestricted Hartree-Fock calculations for the potential energy surface for the reaction N⁺ + H₂ → NH⁺ + H are reported. For the collinear approach of N⁺ to H₂, the ³Σ^? surface has no activation barrier and has a shallow well (ca. 1 eV). For perpendicular approach (C_2v symmetry) the ³B₂ state is of high energy, the ³A₂ state has a shallow well but as the bond angle increases the ³B₁ state decreases in energy to become the state of lowest energy. Neither the collinear nor the perpendicular approaches give adiabatic pathways to the deep potential well of ³B₁ (HNH)⁺.     

The structure of H3O+TiF5−

Oxonium pentafluorotitanate was prepared by the reaction of H₂O with TiF₄ in HF. Single crystal x-ray diffraction studies on H₃O⁺TiF₅- show that the compound crystallizes in monoclinic form. The space group is C2/c and the unit cell dimensions are a = 14.528(5), b = 4.839(1), c = 13.798(5)A^o α = 115.59(5)^o with 8 formula units per unit cell.     

Effect of bending on the predissociation dynamics of N2O+

In this paper we introduce a modified version of the infinite-order sudden approximation (IOSA) for rotational and bending degrees of freedom, together     

Ab initio calculation of the electronic structure and the barrier to pyramidal inversion for H3S+

The electronic structure of H₃S⁺ is examined by ab initio MO calculations (STO 3G) and is compared with those of other XH₃ type molecules. The barrier to pyramidal inversion and the proton affinity of H₂S are calculated to be 34.8 and 225.05 kcal/mol respectively. Computations are made with respect to a model A₃S⁺ which is employed to discuss the barrier to pyramidal inversion of H₃S⁺, where A corresponds to an electromagnetive substituent or an electron donating one.     

An ab initio study of the binding of N2 to Na+ and K+

The binding energies of N₂ to Na⁺ and K⁺ are computed, using the SCF supermolecule approach with extended basis sets together with the counterpoise correction computed in two extreme ways, and supplemented by a perturbation calculation of the dispersion energy. Inclusion of the calculated zero-point energy and the additional correction due to the variation of the correlation in N₂ upon complexation leads to an Na⁺-N₂ binding of ?7.9 to ?8.1 kcal/mole (compared to a measured enthalpy of ?8 ± 0.5) and to a corresponding theoretical value computed for K⁺-N₂ of ?4.6 to ?4.8 kcal/mole.     

Thermal-energy charge transfer of Ar+ with H2O: Internal and kinetic energy of the product H2O+

The reaction of Ar⁺ with H₂O has been investigated at near-thermal energy. The product ions H₂O⁺ and ArH⁺ account for 90 and 10% of the total reaction rate, respectively. Kinetic energy measurements and emission spectroscopy of the H₂O⁺ product ions are reported. It is concluded that at least 60% of H₂O⁺ ions are in the X? state with ≈2.4 eV vibrational energy while up to 40% are in the à state with a mean vibrational energy of 1.4 eV; the à state vibrational distribution has been determined. It is shown that both H₂O⁺ states are populated via an energetically “non-resonant” charge transfer process.     

Solvent extraction of H3O+, NH4+, Ag+, K+, Rb+ and Tl+ into nitrobenzene by using cesium dicarbollylcobaltate in the presence of a hexaarylbenzene-based receptor

From extraction experiments and γ-activity measurements, the extraction constants corresponding to the general equilibrium M⁺(aq) + 1·Cs⁺(nb) \rightleftarrows \rightleftarrows 1·M⁺(nb) + Cs⁺(aq) taking part in the two-phase water–nitrobenzene system (1 = hexaarylbenzene-based receptor; M⁺ = H₃O⁺, NH₄ ⁺, Ag⁺, K⁺, Rb⁺, Tl⁺; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Furthermore, the stability constants of the ML⁺ complex species in nitrobenzene saturated with water were calculated; they were found to increase in the series of Rb⁺ < K⁺ < Ag⁺, Tl⁺ < H₃O⁺, NH₄ ⁺.     

Rate constant measurement for the reaction of D3+ with H2

The rate constant and the product distribution for the reaction of D₃⁺ with H₂ has been measured as a function of the D₃⁺ vibrational energy. In these experiments a mass analyzed beam of D₃⁺ ions is decelerated to less than 0.1 eV and is subsequently injected into an ion cyclotron resonance (ICR) cell where reaction with H₂ may occur. Ion detection is achieved using a conventional oscillator-detector. The number of D₃⁺-D₂ coliisions was varied from 0 to 10 by changing the D₂ pressure in the source of the first stage of the instrument.     

A combined extraction and DFT study on the complexation of H3O+ with a hexaarylbenzene-based receptor

Abstract  

By means of theoretical calculations at density functional level, the complex structure of a hexaarylbenzene-based receptor with Na⁺ was derived. In the resulting complex having C ₃ symmetry, the sodium cation synergistically interacts with the hydrophilic polar ethereal oxygen fence and with the central hydrophobic benzene bottom of the parent receptor via cation–π interaction.     

The geometry of the propynol cation,HC3O+

The geometry of a potential interstellar molecule, the propynol cation, HC₃O⁺, is determined by split-valence plus polarization (6-31G*) SCF method with the inclusion of electron correlation effects by third order Møller—Plesset perturbation theory (MP3). The 6-31G* MP3 geometry is: r_e(CO) = 1.125, r_e(CC) = 1.351, r_e(CC) = 1.214, r_e(CH) = 1.078 A, and thus a B_e of 4.421 GHz.     

Determination of the radiative lifetimes of the b1Σ+ and a1Δ states in NH by ab initio methods

Probabilities for the spin-forbidden transitions from the b¹Σ⁺ and a¹Δ states to the X³Σ^? ground state of NH have been evaluated by a first-order perturbation expansion into S-eigenfunctions Nine ³Π and ¹Π, five ¹Σ⁺ and three ³Σ^? states have been calculated by the MRD CI method at the experimental equilibrium distance of the X³Σ^? state (1.0362 Å) which cover a vertical spectral region of = 100000 cm^?1. The expansion terms of the perturbation sum are spin-orbit coupling coefficients obtained by using the Breit-Pauli one- and two-electron spin-orbit operator. The radiative lifetime of b¹Σ⁺ has been determined in the Franck-Condon approximation to be 72 ms from ab initio data and 97 ms if experimental excitation energies for the low-lying valence states are employed. Recent experiments give a somewhat shorter lifetime for the corresponding 0-0 transition of 53 ms. The lifetime is governed by the transition to the ³Σ^?_±1 level of the non-rotating molecule, borrowing its intensity mainly from the A³Π → X³Σ^? dipole transition. The second possible transition to the Ω = 0 level of the ground state is found to be weak. A similar relation of μ₁/μ₀ is expected for all the hydrogen containing isovalent molecules such as PH and AsH. The radiative lifetime of the a¹Δ state has been calculated to be = 1.7 s. Recent matrix experiments predict a gas-phase lifetime of at least 3 s. Further experimental and theoretical investigations are in progress to clarify this unusual finding that the experimentally determined lifetime is longer than that calculated theoretically.     

A State-selected study of the symmetric charge transfer reaction H2+ + H2

We have measured the relative total charge transfer cross sections of H₂⁺ + H₂ as a function of the vibrational state of H₂⁺, υ′_o = 0–4. using the crossed ion-neutral beam and high-resolution photoionization methods. The experimental results obtained at a center-of-mass collisional energy of 22.5 eV are found to be in excellent agreement with a recent theoretical study.     

Lifetimes of the vibronic Ã2A1 states of H2O+ and of the 3Πi (υ′ = 0) state of OH+

Using the delayed coincidence technique, lifetimes have been measured for some Σ and Π vibronic òA₁ states of H₂O⁺ and for the ³Π_i (υ′ = 0) state of OH⁺ by analysing the decay curves of the òA₁(0, υ′₂, 0) ? X?²B₁ (0, υ″₂, 0) and the ³Π_i(υ′ = 0) ? ³Σ^?(υ″ = 0) emission intensities respectively. The excited molecular ionic states are produced via excitation of H₂O molecules by 200 eV electrons. For H₂O⁺(òA₁) the vibronic Σ levels with υ′₂ = 13 and 15 and the vibronic Π levels with υ′₂ = 12 and 14 have been considered. The radiative lifetimes obtained for these levels have about the same value, namely 10.5(±1) × 10^?6 s. The radiative lifetime for the OH⁺(³Π_iυ′= 0) state is 2.5(±0.3) × 10^?6 s. The lifetimes found in this work for H₂O⁺(òA₁) and OH⁺(³Π_i,υ′= 0) are about ten and three times longer respectively than the corresponding lifetimes given by other investigators [1,2]. The probable reason for this discrepancy is that in the other experiments no attention has been paid to the presence of a large space charge effect. This effect is caused by the positive ions which are created by the primary electron beam.     

Ab initio potential curves for the lowest 1Σ+ and 3Π states of the ion CN+

Ab initio configuration-interaction calculations using a 9s5p|3s2p gaussian basis supplemented with polarization functions are presented for potential curves for the a ¹Σ⁺ and the lowest ³Π state of CN⁺. The two states are very close in energy and calculations at this level do not give an unequivocal indication of the identity of the ground state.     

An ab initio description of the excited states of the reaction O(3P, 1D) + H2 → OH(2Π, 2Σ+) + H. An attempt to describe several potential energy surfaces with constant accuracy

A new aspects of the role of the solvent mode in the photoinduced electron-transfer process of electron donor and acceptor system in polar solvents has been exploited. Taking into account the important fact that the vibrational frequency of the solvent mode in the initial neutral state of the reactants is considerably smaller than that in the final ionic state, we have derived a new formula for the energy-gap dependence of the electron-transfer rate. In this formulation, the activation energy is greatly reduced and the electron-transfer rate is almost independent of the energy gap over a wide down-hill energy region. This qualitative feature explains the experimental results for the relation between the bimolecular quenching rate constant k_w and the standard free-energy change ΔG° associated with electron transfer in the “anomalous region”.     

Luminescence in near-thermal charge exchange. II. He+ + H2O and He+ + D2O

An ICR spectrometer fitted with synchronous photon counting equipment is used to study the emission produced by near-thermal (? 0.1 eV) collisions between He⁺ and H₂O (D₂). Within the investigated wavelength region, 185 to 500 nm, the only significant emission features are the A³Π (υ' ? 3) → X³Σ^? bands in OH⁺ and OD⁺, and the A²Σ⁺ → X²Π(0.0) band in OH and, possibly, in OD. The corresponding excitation rate constants represent only ? 2% of the total He⁺/H₂O (D₂O) charge transfer. The resonant electron-jump model for thermal-energy charge exchange is discussed in the light of recent information on the He⁺/H₂O reaction and on the excited states of H₂O⁺ and their excitation by electron and photon impact on H₂O (D₂O).     

An ab initio study of the potential surface for the reaction H2COH → HCO + H2

The potential surface for the reaction H₂CO⁺H → HCO⁺ + H₂ has been studied by ab initio SCF calculations, using gaussian-type basis functions. A saddle point on the surface has been found, and a reaction path is proposed to explain the observed release of kinetic energy. The energy of activation and ΔE for the reaction have been estimated.