Visible absorptions of potential diffuse ISM hydrocarbons: C${}_9$H${}_9$ and C${}_9$H${}_5$ radicals

The laboratory detection of previously unobserved resonance-stabilized C${}_9$H${}_5$ and C${}_9$H${}_9$ radicals in the supersonic expansion of a hydrocarbon discharge source is reported. The radicals are tentatively assigned as acetylenic-substituted cyclopentadienyl C${}_9$H${}_5$ and vinyl-substituted benzyl C${}_9$H${}_9$ species. They are found to feature visible absorption bands that coincide with a few very weak diffuse interstellar bands toward HD183143 and HD204827.