Laser plus surface-dynamics facility

The objective in this one-year study has been to develop a vacuum ultraviolet (VUV) laser suitable for investigating the simplest of chemical reactions, H + H2 yields H2 + H. This reaction has been fundamental to the development of our understanding of chemical reactions in gases over the past half century, and could come to occupy a similar pivotal role in regard to the elucidation of the molecular dynamics of exchange reactions at surfaces. In order to generate atomic H we have expanded HI from a quartz nozzle (0.1 mm I.D.) into a high vacuum chamber (10 to the -6th power). The density of HI beyond the nozzle could readily be made approx. 0.01 Torr. A Lumonics TE 861-4 excimer laser with unstable resonator operating on KrF at 248 nm (65 mJ/pulse) was used to completely photolyse the HI. When the HI was mixed (ahead of the nozzle) with D2, the reaction H + D2 yields HD + D took place in the jet. A second laser beam was then used (following variable time delay) to probe the reaction product D.