Photodissociation of the dimer ions Ar+2, Ne+2, and (CO2)+2

The tandem quadrupole photodissociation mass spectrometer has been used to study photodissociation reactions of Ar⁺₂, Ne⁺₂, and (CO₂)⁺₂. The cross sections for photodissociation of Ar⁺₂ exhibited a strong dependence on ion source pressure, varying from 2 × 10 ^?18cm² at 0.1 torr to 6 × 10^?19cm² at 0.5 torr. A large photodissociation cross section (2 × 10^?17cm² for the reaction (CO₂)⁺₂ → CO⁺₂+ CO₂ was observed at the red end of the visible spectrum (580–620 nm) suggesting that this may be an important reaction in CO₂ rich planetary ionspheres such as that of Mars.     

Laser induced photodissociation of H+2 and D+2 ions

Photodissociation of H⁺₂ and D⁺₂ has been observed in a crossed beam experiment. A laser used as photon source. The ion and laser beam cross each other inside the laser cavity. The momentum spectra of the resulting H⁺ or D⁺ fragments are recorded with a mass spectrometer. From the spectra the excess kinetic energy is calculated. These values agree with the theoretically expected ones within the experimental error. From the measured intensity distribution the relative population for several vibrational states in the primary ion beam is calculated. Our values deviate from the usual assumed Franck-Condon pattern as well as from the values reported by Dunn. The angular dependence of the fragments is also measured. This dependence indicates a polarization of the primary beam perpendicular to its direction.     

Reactions of O+4 and O+2 with methane

Rate coefficients and products were determined for the title reactions employing a drift tube mass spectrometer apparatus. The implications of these reactions for the ion chemistry of the stratosphere is discussed.     

Vibrational effects in proton and charge transfer in the H+2 + Ar system

Reaction and charge transfer of H⁺₂ + Ar to give ArH⁺ and Ar⁺ have been investigated as a function of H⁺₂ vibrational quantum state and kinetic energy (Ec.m.), using photoionization and guided beam ion optics. Resonance effects are important in charge transfer; proton and charge transfer are closely coupled for Ec.m. 3 eV.     

A theoretical study of the sulphonium cation SH+3

Ab initio Hartree—Fock calculations with STO-3G functions have been performed to determine the structure (1.371 Å and 95.33°) of SH⁺₃ and the proton affinity (≈196 kcal/mol) of H₂S. Inclusion of a sulphur 3d function in the basis has been found essential to give a better geometry of SH⁺₃.     

The ESR spectrum and structure of the dimer radical cation of dimethyl selenide (Me2Se-SeMe+2) in a γ-irradiated single crystal

The dimer radical cation of dimethyl selenide has been identified in a γ-irradiated single crystal of the parent compound, its main (^evenSe) ESR spectrum showing hyperfine coupling to twelve equivalent hydrogens. Also, the relative intensity of the naturally abundant⁷⁷Se satellite spectrum is in agreement with a hyperfine interaction involving two anisotropically equivalent selenium atoms. The principal values and direction cosines of the⁷⁷Se hyperfine andg tensors have been determined and are shown to be satisfactorily interpreted in terms of a centrosymmetric structure, the unpaired electron occupying an antibonding (σ^*) orbital built almost entirely from the p_σ orbitals of the two selenium atoms. Analysis of theg tensor components indicates that the CSeC planes are perpendicular to the direction of the Se-Se bond. It is also shown that the isotropic¹H splitting andg factor obtained previously from solution ESR studies of the dimethyl sulphide dimer cation are consistent with the structure advanced here for the selenium dimer. The results seem to rule out the possibility of any significant d orbital participation in the bonding.     

The structure and energy of SiH+5. comparisons with CH+5 and BH5

Differences between SiH⁺₅ and CH⁺₅ are more significant than the similarities. The proton affinity of SiH₄ exceeds than of CH₄ by ≈25 kcal/mol. but the heat of hydrogenation of SiH⁺₃ is smaller than that of CH⁺₃ by nearly the same amount. Like CH⁺₅ the C₅ structures of SiH⁺₅ are preferred, but SiH⁺₅ is best regarded as a weaker SiH⁺₃—H₂ complex. D_3h, C_2v, and C_4v forms are much higher in energy and SiH⁺₅ should not undergo hydrogen scrambling (pseudorotation) readily, as does CH⁺₅ The neutral BH₅ is only weakly bound toward loss H₂, and the D_3h. C_2v, and C_4v forms are also high in energy. The contral-atom electronegativities, C⁺ > B > Si⁺, control this behavior. The electronegativities also determine the ability to bear positive charges. Thermodynamically. SiH⁺₅ and SiH⁺₃ are more stable than CH⁺₅ and CH⁺₃, respectively; hydride transfer occurs from SiH₄ to CH⁺₃ and proton transfer from CH⁺₅ to SiH₄.     

The SO+2 radical-ion

From the complex overall EPR spectrum of ⁶⁰Co gamma-irradiated pure solid sulfur dioxide the spectrum of the SO⁺₂ radical-ion was selected and the following principal values for the g-tensor obtained: g₁ = 1.9620;g₂ = 2.0026;g₃ = 2.0118 (Δg = ± 0.0005).     

Explanation for the structural differences of S2+4, S04 and S2−4

An explanation for the geometry changes upon successive double reductions of S²⁺₄ (square planar, D_4h symmetry) to neutral S₄ (for which the structure is unknown) and finally to S^2?₄ (non-planar, C₂ symmetry) is given on the basis of orbital eigenvalues and wavefunctions calculated with the self-consistent-field Xα scattered-wave molecular orbital method.     

Laser-induced photodissociation of He+2

The momentum distributions of He⁺ fragments from photodissociation of He⁺₂ ions have been recorded in a crossed-beams experiment. The discrete values of the kinetic energy releases can be predicted from the vibrational spacings in the ground state of the primary ions.     

Vibration intervals for tritiated H+3 and D+3

Ab initio calculated values of fundamental vibrational frequencies and zero-point energies are presented for HTD⁺, D₂T⁺, T₂D⁺, H₂T⁺, T₂H⁺ and T⁺₃.     

Theoretical calculation of the electronic structure and the optical spectrum of CrF2−6

The electronic structure of the CrF^2?₆ cluster has been analyzed by solving the Hartree-Fock equations on several electronic states, at five values of R, the metal-ligand distance in the a_1g vibration. The methodology of J. W. Richardson, T. F. Soules, D. M. Vaugth, and R. R. Powell (Phys. Rev. B4, 1721 (1971)) has been used. The computed R_e is in close agreement with the observed value in alkali hexafluorochromates(IV). The nuclear potentials of the d² triplets are almost parallel to the ground state potential, giving rise to a weak R-dependence of the spin-allowed transitions and a negligible contribution of the a_1g progression to the vibrational structure of the broad bands. The absorption spectrum has been discussed in terms of the results of different SCF calculations. A new assignment is proposed that avoids most of the earlier difficulties of the spectral interpretation. The best calculated spectrum agrees with the one observed in Rb₂CrF₆ within 1.5 kK.     

Synthesis and crystal structure of (ThCu3)(Mn3+2Mn4+2)O12, a new ferrimagnetic perovskite-like compound

Single crystals of [ThCu₃](Mn³⁺₂Mn⁴⁺₂]O₁₂, a ferrimagnetic perovskite-like compound, have been synthesized by hydrothermal conditions at 600°C and 2 kbar. They have been found to be cubic, of space group Im3, with a = 7.359 Å, and isostructural with [NaMn₃](Mn³⁺₂Mn⁴⁺₂)O₁₂. The crystal structure has been refined by single-crystal X-ray diffraction data. The Th⁴⁺ cations are surrounded by slightly distorted icosahedra; the ThO distance is 2.556 Å. The Cu²⁺ cations are also surrounded by 12 oxygens, which are arranged as three mutually perpendicular rectangles of different size, the smallest and the largest of which are almost squares. The three sets of CuO distances are 1.973, 2.800, and 3.238 Å. The octahedral MnO distance is 1.950 Å. A test based on neutron diffraction powder data indicated that the square sites are occupied by only the Cu²⁺ cations.     

The electronic structure of Cu(ethanediimine)+2

Extended-Hückel and multiple-scattering Xα molecular orbital calculations are reported for the Cu(ethanediimine)⁺₂ complex. The results obtained are in agreement. From the calculated electronic transition energies, it is inferred that the lowest excited state is a B₂ state of metal-to-ligand charge-transfer type, confirming resonance Raman results.     

Vibrational studies of BH−4 and BD−4 isolated in alkali halides

Single crystals of alkali halides doped with BH^?₄ and BD^?₄ were grown from the melt. Previously unreported bands in the infrared spectra of BH^?₄ and BD^?₄ isolated in different alkali halides are interpreted in terms of summation bands of internal and external modes of vibration. This has allowed the torsional and translational modes of the impurity ion to be identified. The tetrahedral symmetry of the borohydride ion is retained when it is isolated within alkali halides with the NaCl structure. A reduction of symmetry towards C_3v was observed when BH^?₄ (or BD^?₄) was isolated within lattices with CsCl structure.Raman and far infrared spectra of alkali halide/BH^?₄ systems will be reported for the first time, and high pressure infrared studies of these systems will be described. The effects of pressure in the internal mode, external modes, Fermi resonance and NaCl to CsCl structural phase changes will be discussed.     

Pseudopotential calculations on Rb+2, Cs+2, RbH+, CsH+ and the mixed alkali dimer ions

Semi-empirical pseudopotentials are used in calculating the ground-state potentials curves for single valence-electron molecular ions. Very accurate results are obtained and a number of predictions given. The ionization energies of the neutral dimers are evaluated. A spectroscopic rule enables us to estimate the A ¹Σ⁺ state of KRb and RbCs.     

ESR and structure of SO2Cl−√2

A single crystal ESR study is reported on the radial anion of sulphury chloride. In addition to the main spectrum which can be ananyzed in terms of anisotropic hyperfine coupling to two equivalent chlorines, the satellite spectrum of ³³SO₂Cl^?√₂ has been observed in natural abundance. The isotropic value of ca. 200 G for the ³³S hyperfine splitting corresponds to a spin population of 0.21–0.24 in the 3s orbital of sulphur. From the anisotropic chlorine coupling, a spin population of 0.31 in the 3p orbital on each chlorine atom has been derived. These results are consistent with a C_2v trigonal-bipyramid structure, the unpaired electron occupying a molecular orbital of a₁ representation which is localized to a considerable extent in the σ orbitals of the chlorine ligands in the apical positions. A similar structure is indicated by other results for certain isoelectronic phosphorus-centered radicals.     

AB initio calculations of the stability of the OH+4 and FH+3 ions

Some geometric configurations of the OH⁺₄ and FH⁺₃ ions have been calculated by the SCF MO LCAO method using linear combinations of gaussian lobe functions. The total electronic energies of the systems under study are lower than the sum of the energies for H₂O and H⁺₂ or OH⁺₃ and H, and HF and H⁺₂ or FH⁺₂ and H, respectively.     

Rotational analysis of the 201 and 211 bands in the Ã2Σ+-X̃ 2Π spectrum of N2O+

Analysis of new emission spectra of òΣ⁺-X? ²Π in N₂O⁺, including the forbidden components with Δν₂ = 1, have made it possible to locate all four vibronic components of the ν″₂ = 1 manifold. Principal rotational constants and spinvibronic terms are given. A previous estimate of the Renner parameter is revised to a value of ?0.179 ± 0.002.     

Theoretical study of the N+2 molecular ion

The Equations of Motion method has been applied in the calculation of potential energy curves for the X²Σ⁺_g, A²Π_u and B²Σ⁺_u states of N⁺₂. Results are also reported for a new dissociative ²Σ⁺_g state. The theoretical curves are directly compared with the experimental ones as well as in terms of spectroscopic constants. The applicability of the Equations of Motion method to this type of problem is critically examined and discussed with regard to the choice of basis set, numerical effort and agreement with experiment.