ON THE ROLE OF PI-HYDROGENIC STATES IN LOW-ENERGY IH(UPSILON=0)-COLLISIONS - CONVERGED STATE-TO-STATE CROSS-SECTIONS(I)

The dynamics of the I2H system is studied using the Born-Oppenheimer t ype separation between the light and heavy nuclear motions and assumin g the LEPS hypersurface A of Manz and Romelt. In our previous works, h ydrogenic wavefunctions that describe the motion of the H nucleus for clamped iodine nuclei were restricted to sigma(g,u) symmetries. The pr esent work reports results extended to pi(g,u) symmetries. lt is shown that quasi-diabatic hydrogenic wavefunctions lend themselves to an ea sy determination of new resonances in the dynamics and explain the H-a tom exchange in low energy IH + I collisions. Calculations of the H-at om exchange cross sections restricted to pi(g,u) symmetries show that the IH (upsilon = 0, N= 5) + I channel plays an essential role in the H-atom exchange process. Rotational sigma-pi couplings, approximated b y semi-classical expressions, are found to have negligible effect on t he low energy H-atom exchange process. The present work reports the fi rst converged state-to-state H-atom exchange cross sections in the col lision energy range 0-60 meV. The effect of the rotation of the IH mol ecule on the H-atom exchange process is related to the topology of the electronic hypersurface.