A Study of Na-O2Collisions Using Merging Beams

Abstract

A merging beams technique was used to study two-body collisions of Na and ${\mathrm{O}}_2$. In particular, some processes which resulted in positive ions, and negative ions or electrons were investigated. These processes were endothermic and included charge transfer, ionization, and rearrangement. Interaction energies $W$ were varied from threshold, i.e., several electron volts up to 25 eV. In the center-of-mass system and for processes resulting in ${\mathrm{Na}}^{+}$ formation, scattering of ${\mathrm{Na}}^{+}$ was predominantly at angles less than 90° from the well-defined direction of the reactant Na. For the reaction Na+${\mathrm{O}}_2$→${\mathrm{Na}}^{+}$+${\mathrm{O}}_2^{-}$, a very narrow lab energy distribution of ${\mathrm{Na}}^{+}$ was observed for which scattering of ${\mathrm{Na}}^{+}$ in the center-of-mass system was confined to just a few degrees about the Na direction. For this distribution it was also observed that at least 92% of the excess translational energy of the reactants (i.e., interaction energy minus the endothermicity) was converted into translational energy of the products. Therefore, 8% or less went into internal energy of the products. The cross section for Na + ${\mathrm{O}}_2$→${\mathrm{Na}}^{+}$+${\mathrm{O}}_2^{-}$ leading to the formation of ${\mathrm{Na}}^{+}$ in this narrow energy distribution is called $Q_a$. At or near threshold (i.e., 4.71 eV), $Q_a$ rises from zero and reaches a maximum at about 8 eV. From absolute measurements, $Q_a\approx 0.05$ ${\mathrm{\AA }}^2$ at $W=10\mathrm{}$ eV. The existence of Na${\mathrm{O}}^{+}$, first reported by Rol and Entemann, was confirmed in the study of collisions of Na and ${\mathrm{O}}_2$ leading to rearrangement.