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Configuration interaction calculations have been undertaken in a basis of a thousand projected-valence-bond state functions for 1400 points of the (KrO2)+ ground-state potential energy surface. The calculations involve an l-dependent pseudo-potential for Kr and resort to diagonal corrections of the Hamiltonian matrix prior to CI. The computed dissociation energy (0.13 eV) is smaller than the inferred from photodissociation data (0.33 eV) and the potential surface differs in many respects from the previous empirical ones

Configuration interaction calculations have been undertaken in a basis of a thousand projected-valence-bond state functions for 1400 points of the (KrO2)+ ground-state potential energy surface. The calculations involve an l-dependent pseudo-potential for Kr and resort to diagonal corrections of the Hamiltonian matrix prior to CI. The computed dissociation energy (0.13 eV) is smaller than the inferred from photodissociation data (0.33 eV) and the potential surface differs in many respects from the previous empirical ones

The (HO2)+ molecular ion is used to experiment two approximate procedures which aim at reducing the computation effort that is needed for the determination of potential energy surfaces of ion–molecule charge transfer systems. The two procedures involve configuration interaction (CI) calculations of moderate sizes and are based on diagonal corrections of the electronic Hamiltonian matrix in a basis of projected‐valence bond (PVB) configuration‐state functions (CSF). The PVB‐CSF’s used in practice correspond to a full valence CI for each ionic or neutral partner as well as single excitations accounting for polarization and electron transfer. The diagonal corrections are of two sorts: (i) if insufficiently large orbital expansion bases are used they remove the relative ion–molecule basis set superposition error; (ii) if asymptotic energy levels of the involved neutrals or ions in their ground or valence excited states are misplaced they properly adjust these levels. When applied to (HO2)+ using a minimal or an extended orbital basis set expansion the proposed approaches yield concording results. The results also agree with the effective model potential (EMP) data of Grimbert et al. [Chem. Phys. 124, 187 (1988)] which have proved successful in the description of the H++O2 charge transfer dynamics. Comparison with fragmentary results from MRD‐CI calculations by Vazquez et al. [Mol. Phys. 59, 291 (1986)] and Schneider et al. [Chem. Phys. 128, 311 (1988)] is somewhat mitigated. The method should be particularly useful for bulky ion–molecule systems.

The (HO2)+ molecular ion is used to experiment two approximate procedures which aim at reducing the computation effort that is needed for the determination of potential energy surfaces of ion–molecule charge transfer systems. The two procedures involve configuration interaction (CI) calculations of moderate sizes and are based on diagonal corrections of the electronic Hamiltonian matrix in a basis of projected‐valence bond (PVB) configuration‐state functions (CSF). The PVB‐CSF’s used in practice correspond to a full valence CI for each ionic or neutral partner as well as single excitations accounting for polarization and electron transfer. The diagonal corrections are of two sorts: (i) if insufficiently large orbital expansion bases are used they remove the relative ion–molecule basis set superposition error; (ii) if asymptotic energy levels of the involved neutrals or ions in their ground or valence excited states are misplaced they properly adjust these levels. When applied to (HO2)+ using a minimal or an extended orbital basis set expansion the proposed approaches yield concording results. The results also agree with the effective model potential (EMP) data of Grimbert et al. [Chem. Phys. 124, 187 (1988)] which have proved successful in the description of the H++O2 charge transfer dynamics. Comparison with fragmentary results from MRD‐CI calculations by Vazquez et al. [Mol. Phys. 59, 291 (1986)] and Schneider et al. [Chem. Phys. 128, 311 (1988)] is somewhat mitigated. The method should be particularly useful for bulky ion–molecule systems.

The aim of this work is to study theoretically the dominant mechanism in the population distribution between n=2 of Li and He levels. To be able to account for the experimental findups, "ab-initio" calculations have been performed. These calculations take into account both the rotational and radial couplings.

Presents a theoretical study of the relative populations of Sigma and Pi states associated with Li*(n=2)+He+ and Li++He*(n=2) products that are formed in Li++He collisions at keV energies. A half-collision model is considered where the (1s sigma 22p sigma 2p pi ) 1 Pi molecular state is assumed to be prepared initially (as a result of a primary 2p sigma -2p pi rotational coupling step) and the population-sharing processes occur as the collisional system breaks apart. The corresponding calculations involve six-state and twelve-state atomic-like diabatic representations and are carried out using the impact parameter method. the differential electron capture probability and the Stokes' parameters for Li*(22P) and He*(21P) excitations are determined. The calculated alignment angles gamma (Li,He) and shape parameters are slowly oscillating functions of the collision energy. The differences between the results for Li and He are discussed in terms of the various electron transition mechanisms. Qualitative agreement between theory and experiment is found for gamma (Li) but the comparison for gamma (He) is disappointing.

The aim of this work is to study theoretically the dominant mechanism in the population distribution between n=2 of Li and He levels. To be able to account for the experimental findups, "ab-initio" calculations have been performed. These calculations take into account both the rotational and radial couplings.

Presents a theoretical study of the relative populations of Sigma and Pi states associated with Li*(n=2)+He+ and Li++He*(n=2) products that are formed in Li++He collisions at keV energies. A half-collision model is considered where the (1s sigma 22p sigma 2p pi ) 1 Pi molecular state is assumed to be prepared initially (as a result of a primary 2p sigma -2p pi rotational coupling step) and the population-sharing processes occur as the collisional system breaks apart. The corresponding calculations involve six-state and twelve-state atomic-like diabatic representations and are carried out using the impact parameter method. the differential electron capture probability and the Stokes' parameters for Li*(22P) and He*(21P) excitations are determined. The calculated alignment angles gamma (Li,He) and shape parameters are slowly oscillating functions of the collision energy. The differences between the results for Li and He are discussed in terms of the various electron transition mechanisms. Qualitative agreement between theory and experiment is found for gamma (Li) but the comparison for gamma (He) is disappointing.

The determination of alignment and orientation parameters from differential cross section measurements involving the photon-particle coincidence technique prompts theory to investigate a wide variety of electronic transitions both at small and large distances of approach between the collision partners. A theoretical model is presented with a view to explaining alignment and orientation phenomena related to Li++He*(21P) excitation and Li*(22P)+He+ charge exchange excitation in the prototype Li++He collision. The corresponding discussion is illustrated using a recent ab initio study by the authors