ON THE DYNAMICS OF THE VIBRATIONALLY SELECTIVE ELECTRONIC-ENERGY TRANSFER FROM METASTABLE XENON ATOMS TO NITROGEN MOLECULES

The energy transfer reaction Xe(3P0,2) + N2(X) --> Xe(1S0) + N2(B 3PI( g)) is analyzed by extensive numerical calculations of the dynamics. T he potential energy surfaces used were previously shown to account qua litatively for the experimental findings. The present calculations are aimed at an explanation of the branching ratios between the vibration al levels of the N2(B) product as previously measured at several colli sion energies. The collisions are treated as sudden with respect to mo lecular rotation and the reaction is assumed to be adiabatic on vibron ic states. Those crossings between entrance and exit channels which ar e responsible for the nonadiabatic transitions are identified by symme try analysis and numerical experiments, using the Landau-Zener theory. Information on the strength and radial dependence of the relevant cou pling matrix element is obtained. The separability between vibrational and electronic degrees of freedom is discussed. In certain cases the nonadiabatic transitions are so fast that molecular rearrangement can be neglected (sudden behaviour), while in other cases they are slower than vibrations (adiabatic behaviour). In the sudden limit the Franck- Condon factors between the N2(X) and N2(B) vibrational wavefunctions h ave to be taken into account, but in the adiabatic limit they are unim portant.