S. O. Adamson

Multipartitioning many-body perturbation theory calculations on temporary anions: applications to N−2 and CO−

The multipartitioning form of the second-order many-body perturbation theory for state-selective effective Hamiltonians is adapted to stabilization calculations of temporary molecular anionic states. We restrict our attention to the simplest case of a system composed of a closed-shell-like molecule and an electron. Pilot applications to the description of the 2Πg state of the nitrogen molecular anion and the 2Π state of CO− are reported.

Laser stimulation of low-temperature dissociative recombination of electrons and oxygen molecular ions

AbstractA theory of dissociative recombination of slow electrons and molecular ions in a strong monochromatic light field is developed. The theory takes into account interference between various reaction channels and is constructed in a rigid basis adiabatic with respect to rotation (the approximation of a fixed molecular axis). The mathematical apparatus of the theory is based on the stationary formalism of the matrix of radiation collisions, whose poles correspond to “quasi-energy” states of a composite system. Along with transitions into dissociative configurations, field-induced nonadiabatic transitions into bound intermediate states of valence (non-Rydberg) configurations are considered. As a particular application of the theory, the e− + O2+(2Πg) →

Associative ionization reaction N + O → NO+ + e– in slow collisions of atoms

O(^{2s_1 + 1} l_1 ) + O(^{2s_2 + 1} l_2 )

Application of the Uniformly Charged Sphere Stabilization for Calculating the Lowest 1S Resonances of H

reaction is analyzed. A study of this reaction requires detailed information about the potential curves of the states participating in it with taking into account the external electromagnetic field (l and s are the electronic angular momenta and reaction product spins). For this purpose, the general problem is divided into three stages. At the first stage, the theoretical approach is formulated, and at the second stage, the corresponding potential curves are calculated and the main reaction mechanisms are determined. The third stage should include calculations of the total and differential cross sections. This work is concerned with the first two stages; that is, the adiabatic potential curves of the singlet and triplet dissociative states of the O2** oxygen molecule are calculated, a classification of all possible transition types is given, and reaction mechanisms in the presence of monochromatic laser radiation are determined. The frequency regions of external radiation in which these mechanisms are most effective are found.

AB INITIO FINITE-FIELD TRANSITION MOMENT CALCULATIONS

The possibility of using the uniformly charged sphere with the variable charge and constant radius for accurate phase shift and resonance states parameters calculations is investigated. It is demonstrated on the example of the Hazy-Taylor model problem that the proposed numerical technique provides the relative errors about 1% for the phase shift function and resonance state parameters (energy and width). The choice of the optimal basis set for such calculations is discussed also.

Ab initio calculations of lower resonant states of two-electron systems

The endothermic associative ionization reaction N(2D) + O(3P) → NO** → NO(1Σ+) +e- in slow collisions of the atoms has been considered in terms of the multichannel quantum defect theory. The dependences of the partial and total cross sections of the reaction on the energy of the colliding atoms in the range of 0–0.3 eV have been calculated. It has been shown that the cross sections have a pronounced resonance structure, which is formed as a result of the multichannel interaction of autoionization states of the intermediate Rydberg complex NO** with dissociative states. The temperature dependence of the reaction rate constant is presented. The results are compared with those of other calculations and available experimental data.

Calculation of the parameters of resonance states using stabilization with non-Coulomb potentials

By the example of the lowest resonance state of the H− system, two versions of the stabilization method are considered: with introduction of an external potential into the Hamiltonian and with enlargement of the single-particle function basis. A comparison of the results suggests the possibility of applying these methods to calculating the resonance parameters in many-electron systems.

The application of stabilization and exterior complex scaling methods to calculations of predissociation resonances in the hydrogen molecule

The uniformly charged sphere stabilization method has been used to calculate the lowest 1 S resonances of H −. It was shown that this method is sensitive to the choice of basis set and parameters of the stabilization potential. The conclusion on the suitability of this method for calculating resonance energies and widths is based on the analysis of our computational results.