Orientation effects in H2 dissociation by He2+ impact at vP =1 and 2 a.u.

We have investigated the dependence of two electron processes leading to dissociation on the orientation of the H₂ molecule, by measuring differential cross sections for proton fragment emission in coincidence with the outgoing projectile charge state. Proton energy spectra (4-15eV) emerging at angles 10° and 90° were obtained for He⁺ and He⁰ charge states from He²⁺+H₂ collisions at E_P=25 and 100keV/amu ( v_P=1 and 2a.u. ). By means of the Franck-Condon approximation we found the contribution to the proton emission from the 2pπ_u , 2sσ_g , 2pσ_u , and Coulomb explosion dissociation channels, allowing us to obtain cross sections for double capture, transfer ionization, and transfer excitation processes. Cross sections for double ionization and ionization plus excitation were also obtained from the measured data. The results were discussed on the basis of a two-step model within the independent electron approximation, using a perturbative approach for the single capture process.