Evanescent wave cavity ring-down spectroscopy for probing surface processes

Sub-monolayer detection of adsorbed I-2 is demonstrated with the cavity ring-down technique by using intra-cavity total-internal reflection to generate and evanescent field that probes the adsorption process. A precision, fused-silica Pellin-Broca prism with ultra-smooth facets (surface roughness similar to 0.05 nm r.m.s) is employed to provide the intra-cavity TIR. The known cross-section for the (1) Sigma(g)(+) --> 3 Pi(n) transition of I-2, which is largely invariant between pressure-braodened gaseous weakly chemisorbed, and liquid states, provides quantification of senstitivity. A minimum detectable coverage of similar to monolayer is determined at a weakly absorbed probe wavelength. (C) 1997 Elsevier Science B.V.