Laser-Enhanced Lyman-αProduction in Collisions between Hydrogen Ions and Sodium Atoms

The first measurement is reported of the absolute cross section as a function of kinetic energy for a process involving a state-selected excited reactant, namely near-resonant ${\mathrm{H}}^{+}$-$\mathrm{Na}\mathrm{}\left(3p\right)\mathrm{}$ charge exchange. The ion-beam experiments show enhanced production of $L\alpha$ from ${\mathrm{H}}^{+}$-Na when the sodium is irradiated with laser light tuned to a $D$ line. The results presented here demonstrate unambiguously that of ${\mathrm{H}}^{+}$, ${\mathrm{H}}_2^{+}$, and ${\mathrm{H}}_3^{+}$, only ${\mathrm{H}}^{+}$ leads to enhancement; however, the effect occurs only for energies below 30 eV.