Laser-controlled dissociation and ionization pathways in electronically excited AsH3

Experiments involving 193 nm AsH3 excitation are described. With ≥25 ns delay between the firing of photolysis and probe lasers, product H atoms are detected by two-frequency, two-photon ionization (121.6 nm+364.7 nm) via Lyman-α. However, temporally overlapping the photolysis and ‘‘probe’’ beams enables ionization to complete with dissociation. The resulting AsH+x signal displays a marked dependence on the near-UV frequency, and AsH+x peaks are accompanied by dips in the H-atom signal. Delay and near-UV frequency control the competition between the different pathways, and the overall effect is both easily induced and macroscopic. Applications may be found in the photoassisted growth of semiconductor materials.