The advantages of the adsorbed state for spectral studies of the ozonolysis mechanism are illustrated by ozone reaction with ethylene on silica. The sample with preadsorbed ethylene or C2D4 was brought into contact with O-16(3), O-18(3), or mixed O-16(3)/O-18(3) from the solution in liquid oxygen at 60-77 K or from the gas phase at 77 K. The method enables us to detect the first products of ozonolysis, including primary and secondary ozonides or formaldehyde, arising already at 77 K or below and to follow their transformations in a wide temperature interval, not available for solid matrices or solutions. Formaldehyde, which should arise at the intermediate step of the reaction, is formed when an excess of ozone is admitted from the gas phase. It is supposed that O-3 reaction with dioxymethyl (Criegee intermediate) prevents its recombination with formaldehyde, providing the stabilization of the latter.