Non-adiabatic effects beyond the rotational coupling in H⁺+H collisions

The H + -H collisional system is revisited in order to study the nature and the effects of the non-adiabatic 2p sigma u -np sigma u radial couplings in the range of internuclear distances 0<R<2 a 0 . To investigate whether these couplings reflect pseudo-crossings caused by the 'super-promotion' of an exotic state the authors build alternatively diabatic representations that preserve the characteristics of the two-centre separated-atom wavefunctions or those of the single-centre united-atom wavefunctions. It is found that none of the considered approaches supports a curve-crossing view. They demonstrate that the common bell-shaped form of the (2p sigma u mod delta / delta R mod np sigma u ) matrix elements is not an exclusive property of the 2p sigma u state and the authors uncover a duplication property of all the (np sigma u mod delta / delta R mod n'p sigma u ) non-adiabatic couplings. Finally, calculations of the probabilities of electron transitions due to these couplings show that a 10% leakage from the adiabatic 2p sigma u state does occur at small impact parameters at collision energies above 1 keV.