Surface pressure/area per molecule (pi-A) isotherms of arachidic acid monolayers on subphases containing various Pt-II and Pd-II amine complexes were measured. Metal arachidate LB films derived from these monolayers were deposited on gold-coated glass and mica substrates. The reactions of these films with H2S were investigated using UV-visible, grazing angle Fourier transform infrared, and X-ray photoelectron spectroscopic techniques and atomic force microscopy. The absorbance onsets of the H2S exposed films are dramatically blue shifted relative to the bulk bandgaps of PtS and PdS consistent with the formation of particles in the "Q state" size regime. Atomic force microscopy images of palladium arachidate films on mica exposed to H2S revealed particles with an average diameter of 4.8 nm.