Ultraviolet absorbers in the Venus clouds

Some absorption features in the ultraviolet spectrum of Venus observed by the OAO-2 cannot be interpreted in terms of H2SO4. Carbon suboxide polymer has a yellow colour and absorption at 2000 A. Fine graphite grains have an absorption band at about 2175 A as is well known in the case of the interstellar extinction curves. A mixture of these substances which is inevitably formed in the Venus atmosphere by photochemical reactions is the best candidate for explaining the Venus absorption features in the ultraviolet.