Translational spectroscopy of N+ fragments from 5 keV collision-induced dissociation of N2+ ions by helium

Collision-induced dissociation of a 5–10 keV N₂⁺ beam impinging on a helium target has been reinvestigated by translational spectroscopy. The laboratory kinetic energy distribution of N⁺ fragments exhibits height structures on a continuum. They correspond to N⁺ and N fragments ejected in the c.m. frame with kinetic energies W of 4.75, 6.4, 6.8 and 8.1 eV and they are interpreted as transitions into excited states of N₂⁺ lying at more than 30 eV above the ground state of N₂. The experimental W distribution extending over 12 eV is compared to distributions calculated using the model of vertical Franck—Condon electronic excitation with different assumptions for the initial and final states.     

State selected ion-molecule reactions

A summary is given of recent state selected experimental data on charge transfer in the system [N₂+Ar]⁺. New results are reported on the reaction of Ar⁺(² P _J )+N₂, obtained at Orsay by threshold photoelectron-photoion coincidence techniques employing synchrotron radiation. Recent theoretical models dealing with [N₂+Ar]⁺ charge transfer are briefly discussed in regard to their capability to account for the most characteristic experimental observations.     

Simple molecular wavefunctions with correlation corrections II

The potential curves for the ground state of Li₂ (¹ _g ⁺ ) and FH (¹ _g ⁺ ) are computed. The correlation energy is calculated using a functional of the one- and two-electron density matrices derived from an MC SCF reference wavefunction and is added to the reference energy to obtain a correlated potential curve.     

Some ab initio calculations related to the predissociation of the C2Σu+ state of N2+

Ab initio calculations in the “first-order wavefunction” CI approximation have been performed for several states of N₂⁺ with ²Σ_u⁺, ²Σ_u^?, ⁴Π_u symmetry. A calculation of the electronic factor of the vibronic interaction between the B²Σ_u⁺ and C²Σ_u⁺ states seems to support the suggestion of Tellinghuisen and Albritton that the C state is predissociated by the continuum of the B state through nuclear momentum coupling.     

Ab initio study of N2O+. Angular dependence of the 14A″(4Π) potential

The 1⁴A″(⁴Π) state of N₂O⁺ is found to be the most stable at bent conformations of the nuclei. Ab initio SCF, MC SCF, and MC SCF CI calculations with a double-zeta basis and typical bond-length values for R_NN and R_NO all yield minimum energy angles near 126°. The energy lowering is such that the total energy of N₂O⁺ (1⁴A″, 126°) is very near that of the lowest O, N₂ asymptote, ⁴S, X ¹Σ_g⁺. These results are shown to imply that the ionospheric reaction O⁺ + N₂ → NO⁺ + N, the rate-determining step in the electron removal reaction network, is adiabatic on the potential surface of the 1⁴A″ state.     

“Magic” losses of one to five N2 molecules from metastable N+2n clusters

SIMS and FAB of solid N₂ generated large N_2n⁺ clusters (N₄⁺ -N⁺₅₄) which showed three types of metastable decay: (i) loss of a single N₂ molecule, assigned to ordinary (“thermal”) metastability, (ii) nearly total disintegration, assigned to radiationless decay of an electronically excited state, and (iii) “magic” losses of very specific small numbers of N₂ molecules, assigned to N₂(v = 1) vibrational relaxation by use of isotope effects. Average N₂ binding energies are estimated.     

Analysis of approximations and errors in equations of motion method calculations

We analyze a number of fundamental questions associated with the use of a finite one-particle orbital basis in equations of motion (EOM) method calculations of excitation energies etc., of atomic and molecular systems. This approximation yields an approximate n_e-electron ground state and say, N excited states, while there are (N + 1)² different possible basis operators for EOM calculations. We show that sets of at most 2N basis operators can contribute to the EOM calculations. Any set of 2N basis operators, satisfying certain conditions, provides the exact EOM energies which are equivalent to complete configuration interaction results within the same orbital basis. We investigate the use of particle-particle shifting operators which are not employed in EOM calculations in model calculations on He with operator bases smaller than the complete 2V to consider the convergence of the expansion. The dependence of EOM calculations on the quality of the approximate ground state wavefunction is studied through calculations for Be where additional support is provided for the frequent need for multiconfigurational zeroth order reference functions (as corrected perturbatively). Excited state EOM wavefunctions from EOM calculations are shown to not necessarily be orthogonal to either the exact or approximate ground state wavefunction, suggesting implications in the use of EOM methods to evaluate excited state properties. The He and Be examples and a simple two-level problem are also utilized to illustrate questions concerning the use of the EOM equations to obtain an iteratively improved ground state wavefunction.     

Ab initio calculation of the mobility of C+(2P) and C+ (4P) in helium

The mobility of the ²P ground state and the ⁴P excited state of C⁺ in helium have been calculated using the two-temperature theory of ion transport and HeC⁺ interaction potentials calculated at the MP4SDQ/6311 + G(3df,3pd) level of theory. Agreement with experimental data is very good. The results confirm a recent experimental observation of the ⁴P state of C⁺.     

On the origin of energy barriers in the excited states of He2

The A ¹Σ⁺_u and C ¹Σ⁺_g states of He₂ have been examined using self-consistent (spatially projected) generalized valence bond (GVB) wavefunctions. We find both states to have humps (0.06 and 0.22 eV, respectively) at large R (3.1 Å and 2.1 Å, respectively). The repulsive nature of these states at large R results from non-bonding interactions between the singlet pairs of orbitals located on different centers. For R smaller than the size of the excited He orbital (2s or 2p), the state becomes attractive if the symmetry is such that the wavefunction can build in attractive He⁺₂(²Σ⁺_u) character.     

Cation exchange membranes as solid solutions

The ion exchange equilibrium between KCl and SrCl₂ solutions and the cation selective membrane CR61 AZL386 has been examined. Equilibrium isotherms are measured for membrane—electrolyte equilibria for two total concentrations of Cl^?in the electrolyte solution and at three different temperatures. The results show that Sr²⁺ is strongly preferred to K⁺ in the membrane. Selectivity increases with temperature in the range 10°C to 40°C. It decreases with increasing total concentration from 0.01 N to 0.03 N. Electrolyte absorption in the membrane was not detected for the experimental conditions used. Contents of water in the membrane is constant for external salt concentrations between 3 x 10^?8N and 3 x 10^?2N. The difference in water content between the pure K form and the pure Sr form is approximately 5%.A thermodynamic treatment of ion exchange is presented. The thermodynamic equilibrium constant for the exchange reaction 2 KR + SrCl₂ = SrR₂+ 2 KCl has been determined by two different integration procedures, R being an ion exchange site in the membrane. The variations of the thermodynamic functions ΔG_mix, ΔH_mix and ΔS_mix are calculated from experimental data for an assumed mixing process of membranes in the pure forms.Activity coefficients for the membrane components are calculated from experimental data. Results are compared to two lattice models. A model with a random distribution of K⁺, Sr²⁺ and a vacant site seems preferred at low concentration of Sr²⁺. At high concentrations, Sr²⁺ and the vacant site associate.     

Oxidations with alkaline permanganate using monovalent thallium for the back-titration: Estimation of trivalent arsenic

In absence of Ba⁺² ions arsenite reduces KMnO₄ in alkaline medium to MnO₂ without the appearance of an inflection at the manganate state. Reduction could be checked at the manganate in presence of 1N NaOH and Ba⁺² equal to 3 times that equivalent to MnO₄^-2 and arsenate, and when dilute arsenite solutions are applied viz.0.02N In absence of Ba⁺² ions the end-points are attained later than the MnO₂ stage except in 2–3N NaOH. In presence of telluric acid good results are obtained at all alkalinities whence reduction is checked at Mn⁺⁴.As⁺³ could be estimated also by mixing with KMnO₄ either in the presence of Ba⁺² ions + 1N NaOH or in absence of Ba⁺² ions + I.5–3N NaOH and back-titrating the excess oxidant with monovalent thallium.     

Theoretical study of structure and stability of h+x (h2)n clusters

The ion clusters H⁺X· (H₂)_n (X = N₂, CO, O₂ and H₂ andn = 0, 1, 2) are investigated by means of SCF and CI computations in a double-zeta plus polarization gaussian basis It is found that hydrogen molecules attack the proton of H⁺X perpendicularly. The calculated stabilization energies are in agreement with experimental values of δH⁰.     

Conformational study of the structure of free 12-thiacrown-4 and some of its cation metal complexes

Conformational search of 12-thiacrown-4, 12t4, was performed using the CONFLEX method and the MMFF94S force field whereby 156 conformations were predicted. Optimized geometries of the 156 predicted conformations were calculated at the HF, B3LYP, CAM-B3LYP, M06, M06L, M062x and M06HF levels using the 6-311G** basis set. The correlation energy was recovered at the MP2 level using the same 6-311G** basis set. Optimized geometries at the MP2/6-311G** level and G3MP2 energies were calculated for some of the low energy conformations. The D ₄ conformation was predicted to be the ground state conformation at all levels of theory considered in this work. Comparison between the dihedral angles of the predicted conformations indicated that for the stability of 12t4, a SCCS dihedral angle of 180° requirement is more important than a gauche CSCC dihedral angle requirement. Conformational search was performed also for the 12t4?CAg⁺, Bi³⁺, Cd²⁺, Cu⁺ and Sb³⁺ cation metal complexes using the CONFLEX method and the CAChe-augmented MM3 and MMFF94S force fields. Conformations with relative energies less than 10?kcal/mol at the MP2/6-31+G*//HF/6-31+G* level, with double zeta quality basis set on the metal cations, were considered for computations at the same levels as those used for free 12t4, using also the 6-311G** basis set. The cc-pVTZ-pp basis set was used for the metal cations. The predicted ground state conformations of the 12t4?CAg⁺, Bi³⁺, Cd²⁺, Cu⁺ and Sb³⁺ cation metal complexes are the C ₄, C ₄, C ₄, C _2v and C ₄ conformations, respectively. This is in agreement with the experimental X-ray data for the 12t4?CAg⁺ and Cd²⁺ cation metal complexes, but experimentally by X-ray, the 12t4?CBi³⁺ and Cu⁺ cation metal complexes have C _s and C ₄ structures, respectively.     

Potential energy curve of 1Σ+ Li+/He

The potential energy curve of the system Li⁺/He has been determined with moderately large basis sets for 0.5 ? r ? 10.0 a₀ both at the SCF level and including correlation. The present SCF results predict a deeper well (?0.00248 au) at a smaller r(3.66 a₀) compared with earlier calculations. Correlation deepens the well further (?0.00274 au), but pulls it inward slightly (3.63 a₀). In the repulsive part the calculated curve lies above the experimental one, especially at shorter distances. A similar behavior has been noted in the systems Li⁺/H₂, Li⁺/CO and Li⁺/N₂, suggesting that the experimental determinations may underestimate the interaction in this region by 10–20%.     

Time-dependent close coupling for vibrational excitation in three dimensions: Application to H+ - H2

Impact parameter calculations for the non-reactive H⁺ + H₂ (n_i = 0) → H⁺ + H₂ (n_f) collision are reported for energies 10 eV ? E_cm ? 200 eV describing the rotational motion of the molecule in the sudden limit. The time-dependent Schrödinger equation for the vibrational motion has been solved by close coupling techniques expanding the vibrational wavefunction into both harmonic and numerically exact H₂ bound states. The convergence in vibrational basis sets, where up to six vibrational levels are considered, becomes worse with decreasing energy and increasing inelasticity. Furthermore, the harmonic wavefunctions are not suitable over a large range of energies to calculate proper cross sections. The various integral and differential cross sections have been compared with the classical results of Giese and Gentry.     

Theoretical investigations of the electronic states of porphyrins. II. Normal and hyper phosphorus porphyrins

Ab initio methods have been used to calculate the ground and excited states of “normal” and “hyper” porphyrins. Perturbation theory and CI methods were used to determine differential ground and excited-state correlation effects for [P^v(P)F₂]⁺ and [P^III(P)]⁺. A comparison is made to the INDO /S /CI predicted wavefunctions and spectra and to the experimental spectra of closely related molecules. The “hyper” [P^III(P)]⁺ calculations show some very low energy electronic transitions which provide an explanation for an anomalous “red” band in the spectrum and for the lack of fluorescence. Ab initio calculations also predict that (1) the lowest energy ¹A₁ state is a two-configuration wavefunction which can be described as a diradical, (2) the two lowest-energy singlet excited states are double excitations from the closed shell SCF configuration, and (3) a ³B₂ state is very close in energy to the lowest ¹A₁ state.