We present calculations of cross sections for one-and two-electron processes in collisions of H + , He 2+ , and C 6+with water molecules in the framework of the Franck-Condon approximation. We employ an independent-electron method and a classical trajectory Monte Carlo approach. Anisotropy effects related to the structure of the target are explicitly incorporated by using a three-center model potential to describe the electron-H 2 O + interaction. We derive scaling laws with respect to the projectile charge. We also estimate cross sections for molecular fragmentation subsequent to electron removal.

The basis and workings of a very useful technique in the treatment of atomic collisions is explained, which is the introduction of a common translation factor in the framework of close-coupling expansions. A historical review of the subject is presented, together with a description of the properties of the factor, and a detailed illustration of its performance.

We describe an implementation of the vibro-rotational sudden approximation eikonal (SEIKON) method to treat collisions between ions (atoms) and diatomic molecules at impact energies such that a semiclassical eikonal approximation can be applied to treat the relative motion of the colliding species, and a close-coupling molecular expansion is able to accurately represent electronic transitions. Our method, which does not make use of Franck - Condon-type approximations, allows us to evaluate vibrationally resolved charge-transfer and excitation cross sections, as well as total cross sections for transitions to the vibrational continuum. The implementation is illustrated with calculations of cross sections for single-charge transfer, vibrational excitation, and transfer dissociation in , and DT collisions. The validity of the Franck - Condon approximation for these reactions is studied.

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Total and n-partial cross sections for charge transfer in Be 4+ + H(1s, 2s) collisions are calculated for collision energies between 2.5 eV amu −1 and 25 keV amu −1 . A molecular expansion is employed, and semiclassical and quantal calculations are carried out including a common translation factor and a common reaction coordinate, respectively. The comparison between quantal and semiclassical cross sections and transition probabilities is discussed.