ULTRAVIOLET-SPECTRA OF QUENCHED CARBONACEOUS COMPOSITE DERIVATIVES - COMPARISON TO THE 217-NANOMETER INTERSTELLAR ABSORPTION FEATURE

QCCs (quenched carbonaceous composite) are amorphus carbonaceous mater ials formed from a hydrocarbon plasma. We present the UV-visible spect ra of ''filmy QCC'' (obtained outside of the beam ejected from the hyd rocarbon plasma) and ''dark QCC'' (obtained very near to the beam) for comparison to the interstellar extinction curve. When filmy QCC is he ated to 500-700-degrees-C (thermally altered), the wavelength of the a bsorption maximum increases from 204 nm to 220-222 nm. The dark QCC ha s an absorption maximum at 217-222 nm. In addition, the thermally alte red filmy QCC has a slope change at about 500 nm which resembles that in the interstellar extinction curve. The resemblance of the extinctio n curve of the QCCs to that of the interstellar medium suggests that Q CC derivatives may be representative of the type of interstellar mater ial that produces the 217 nm interstellar medium feature. The peak ext inction of the dark QCC is higher than the average interstellar extinc tion curve while that of the thermally altered filmy QCC is lower, so that a mixture of dark and thermally altered filmy QCC can match the p eak extinction observed in the interstellar medium. It is shown from e lectron micrographs that most of the thermally altered filmy QCC is in the form of small grainy structure less than 4 nm in diameter. This s hows that the structural unit causing the 217-222 nm feature in QCC is very small.