We present direct experimental evidence for the existence of a surface
-bound state of partially hydrated SO2 on water. Surface second harmon
ic generation (SHG) and static surface tension measurements are used t
o examine the SO2 surface coverage as a function of its bulk aqueous c
oncentration. The results indicate a Langmuir-type adsorption of SO2 a
t the air-water interface. These experiments represent the first repor
t of the application of surface SHG techniques to detect gas adsorptio
n onto a liquid surface.