Ab initio adiabatic and diabatic surfaces of the ground and the first excited electronic states have been computed for the H⁺ + CO system for the collinear ($\gamma = 0^\circ$) and the perpendicular (γ = 90°) geometries employing the multi-reference configuration interaction method and Dunning's 𝑐𝑐-𝑝VTZ basis set. Other properties such as mixing angle before coupling potential and before coupling matrix elements have also been obtained in order to provide an understanding of the coupling dynamics of inelastic and charge transfer process.

An $ab$ initio study on the low-lying potential energy surfaces of H⁺ + O₂ system for different orientations (𝛾) of H⁺ have been undertaken employing the multi-reference configuration interaction (MRCI) method and Dunning's $cc-p$VTZ basis set to examine their role in influencing the collision dynamics. Nonadiabatic interactions have been analysed for the $2 \times 2$ case in two dimensions for 𝛾 = 0°, 45° and 90°, and the corresponding diabatic potential energy surfaces have been obtained using the diabatic wavefunctions and their CI coefficients. The characteristics of the collision dynamics have been analysed in terms of vibrational coupling matrix elements for both inelastic and charge transfer processes in the restricted geometries. The strengths of coupling matrix elements reflect the vibrational excitation patterns observed in the state-to-state beam experiments.

Quantum mechanical study of vibrational state-resolved differential cross sections and transition probabilities for both the elastic/inelastic and the charge transfer processes have been carried out in the H⁺ + O₂ collisions at the experimental collision energy of 23 eV. The quantum dynamics has been performed within the vibrational close-coupling rotational infinite-order sudden approximation framework employing our newly obtained quasi-diabatic potential energy surfaces corresponding to the ground and the first excited electronic states which have been computed using ab initio procedures and Dunning’s correlation consistent-polarized valence triple zeta basis set at the multireference configuration interaction level of accuracy. The present theoretical results for elastic/inelastic processes provide an overall agreement with the available state-selected experimental data, whereas the results for the charge transfer channel show some variance in comparison with those of experiments and are similar to the earlier theoretical results obtained using model effective potential based on projected valence bond method and using semi-empirical diatomics-in-molecules potential. The possible reason for discrepancies and the likely ways to improve the results are discussed in terms of the inclusion of higher excited electronic states into the dynamics calculation.

We present restricted geometry (collinear and perpendicular approaches of proton) ab initio three dimensional potential energy surfaces for H⁺+ CN system. The calculations were performed at the internally contracted multi-reference configuration interaction level of theory using Dunning’s correlation consistent polarized valence triple zeta basis set. Adiabatic and quasidiabatic surfaces have been computed for the ground and the first excited electronic states. Nonadiabatic effects arising from radial coupling have been analyzed in terms of nonadiabatic coupling matrix elements and coupling potentials.

The global adiabatic and quasidiabatic potential energy surfaces for the ground and first three excited (1−4³ A^" ) electronic states of H⁺+ O₂ system are reported on a finer grid points in the Jacobi coordinates using Dunning’s cc-pVTZ basis set and internally contracted multi-reference (single and double) configuration interaction method. Ab initio procedures have been used to compute the corresponding quasidiabatic surfaces and radial coupling potentials which are relevant for the dynamical studies of inelastic vibrational excitation andcharge transfer processes. Nonadiabatic couplings arising out of relative motion of proton and the vibrational motions of O₂ between the adiabatic electronic states have also been analyzed.

A new ground electronic state potential energy surface of Li⁺ + N₂ system is presented in the Jacobi scattering coordinates at MRCI level of accuracy employing the augmented correlation-consistent polarized valence quadrupole zeta (aug-cc-pVQZ) basis set. An analytic fit of the computed ab initio surface has also been obtained. The surface has a global minimum for the collinear geometry at the internuclear distance of N₂, r = 2.078a₀, and the distance between Li⁺ and N₂, R = 4.96a₀. Quantum dynamics studieshave been performed within the vibrational close coupling-rotational infinite-order sudden approximation at E_c.m = 3.64 eV, and the collision attributes have been analyzed. The computed total differential crosssections are found in quantitative agreement with those available from the experiments at E_c.m = 3.64 eV. The other dynamic attributes such as angle dependent opacities and integral cross-sections are also reported.Preliminary rigid-rotor and vibrational–rotational coupled-state calculations at Ec.m.= 2.47 eV also support the experimental observation that the system exhibits a large number of rotational excitations in the vibrational manifold v = 0