Associative ionization in laser-excited sodium 3p+3d collisions

Collisions of laser-excited Na(3p) and stepwise laser-excited Na(3d) atoms in a single effusive atomic beam have been observed to result in Na2+ ion formation: Na(3p)+Na(3d)→Na2++e−. The cross-section for this process is measured to be approximately 15 times larger than the familiar Na(3p)+Na(3p)→Na2++e− associative ionization reaction, at relative collision velocities of approximately 300 m/s. Theoretical models discussed here are qualitatively consistent with the experimental results.