Photostimulated desorption of NO chemisorbed on Pt(100) at 193 nm

Photostimulated desorption of NO chemisorbed on a Pt ( 100) surface at 80 and 300 K has been studied with an ArF excimer laser (λ = 193 nm) and a positive-ion measurement system. NO⁺ is the only ion species observed when a NO-saturated Pt( 100) surface is irradiated with laser light. The NO⁺ yield is proportional to the third power of laser fluence. The translational-energy distribution of the NO⁺ ions is independent of laser fluence. We propose a two-step model as the most probable NO⁺ formation mechanism. The first step is desorption of neutral NO induced by valence-electron excitation in chemisorbed NO with one-photon absorption. Then, the desorbed NO is ionized in the vicinity of the surface via the two-photon nonresonant ionization process. Relatively large desorption cross sections estimated from the decay of the NO⁺ yield support the above NO ⁺ formation mechanism.