A. Sakata

High-resolution spectra of the 3.29 micron interstellar emission feature - A summary

High spectral resolution observations of the 3.29-micron interstellar emission feature show two types of profiles. Type 1 has a central wavelength of 3.289-micron and is observed in extended objects such as planetary nebulae and H II regions. Type 2 has a central wavelength of 3.296 microns and is observed around a small number of stellar sources. Type 2 has a full width at half-maximum of 0.020 micron; Type 1 has a broader FWHM, perhaps as much as 0.042 micron, but this is uncertain because of contamination by Pf(delta) emission. These profiles are tabulated for comparison to laboratory data. It is found that no proposed identification for the 3.29-micron emission feature definitely matches the observational spectra, although amorphous aromatic materials and heated polycyclic aromatic hydrocarbons tend to fit the best.

Infrared spectrum of quenched carbonaceous composite (QCC). II. A new identification of the 7. 7 and 8. 6 micron unidentified infrared emission bands

Infrared spectrum of oxidized quenched carbonaceous composite (QCC) is presented. In addition to the features seen in unoxidized QCC, new features appear at 7.7 and 8.6 microns and the strengths of the features at 6.2, 7.3, and 11.4 microns increase. The infrared features of oxidized QCC are in good agreement with nine of 11 members of the unidentified infrared (UIR) emission bands. The absorption bands of QCC are all broad without fine structure, clearly different from sharp bands of molecules. The 7.7 and 8.6 micron features can be attributed to a cross-conjugated ketone molecular structure. A possible identification of the UIR 7.7 and 8.6 micron bands with this structure is discussed. The present results indicate that oxygen can play an important role in the structures of the UIR emitting material as well as carbon and hydrogen. 29 references.

Quenched carbonaceous composite : fluorescence spectrum compared to the extended red emission observed in reflection nebulae

The photoluminescence (fluorescence) of a film of the laboratory-synthesized quenched carbonaceous composite (filmy QCC) is shown to have a single broad emission feature with a peak wavelength that varies from 670 to 725 nm, and coincides with that of the extended red emission observed in reflection nebulae. The rapid decay of the filmy QCC red fluorescence in air and of the stable blue fluorescence of the filmy QCC dissolved in liquid Freon suggests that the red fluorescence originates from the interaction of active chemical species and aromatic components in the filmy QCC. A material similar in nature to that of the filmy QCC may be a major component of interstellar dust.

Quenched carbonaceous composite. III. Comparison to the 3. 29 micron interstellar emission feature

Laboratory data are presented showing that oxidized f-QCC, after heating to 500 C, has a 3.29 micron absorption feature that matches precisely the wavelength of the 3.29 micron interstellar emission feature. In addition, the width of the f-QCC (filmy quenched carbonaceous composite) feature is close to that of the 3.29 micron emission feature observed in NGC 7027, Orion, and IRAS 21282 + 5050. Laboratory spectra of polycyclic aromatic hydrocarbons (PAHs) were also obtained, and comparison of the f-QCC and PAH absorption spectra to that of the 3.29 micron emission feature indicates that the f-QCC provides a much better match. It is thus suggested that f-QCC is representative of the class of material giving rise to the emission features in the interstellar medium. 31 refs.

Trapped H2O in SiO condensate - An explanation for the 3 micron band observed toward the Galactic center

An SiO condensate containing trapped and adsorbed H2O was produced in the laboratory. The SiO condensate is not a silicate; it is an amorphous silicon suboxide material. The micron absorption of trapped H2O in this condensate matches very closely the 3 micron absorption band of the Galactic center source IRS 7. 19 refs.

Comparison of the absorption curves of soots, pitch samples and QCCs to the interstellar extinction curve

Abstract QCC (Quenched Carbonaceous Composite) is an amorphous carbonaceous material formed from a hydrocarbon plasma. In a previous paper (Sakata et al., Astrophys. J.430, 311–316, 1994), we have studied two forms of QCC: a dark QCC component located near the plasmic beam and a thermally-altered filmy QCC. Both types of QCC derivatives show an absorption feature near 217 nm, but with different extinction magnitude. A mixture of dark QCC and thermally-altered filmy QCC can explain the variations in the interstellar peak extinction. In this paper we show that soot produced from methane. methane-hydrogen gas mixtures and specially produced pitches have a broad extinction feature centered at about 217 nm. The extinction magnitude of the soots and the pitches is lower than that of the average interstellar extinction curve. We discuss the cause of the 217 nm extinction feature of soot, pitches and QCCs, and we suggest that short peripheral carbon chain structures containing π electron conjugation give rise to the 217 nm extinction feature.

Chemical, optical, and infrared properties of quenched carbonaceous composites (QCCS)

Quenched carbonaceous composite (QCC) was synthesized by quenching the plasma of methane gas. Chemical properties as well as optical and infrared spectra of the QCC and “oxidized” QCC were measured. Good agreement of the IR spectra of the QCCs to the unidentified infrared (UIR) emission bands was obtained. Correspondence of their features to molecular structures in the QCC was estimated. It is concluded that a “cross-conjugated ketone” structure (CCK) caused the 6.2, 7.7, and 8.6 μm features and “solo” H atoms on carbon are responsible for the 3.3 and 11.3 μm features.

Simulation of the Formation of Dust Grains in Space by a Plasma Jet Apparatus

Using a vacuum-tight plasma jet apparatus operated below one atmosphere, the condensation of solid particles in space was experimentally simulated. Atomized reactant gases consisting of Si, O, C, and H atoms generated in the plasma flame were injected into a reactor chamber filled with Ar gas of 200 Torr, and quenched into solid particles. The formed grains had irregular shapes and their sizes were smaller than 20 nm. X-ray diffraction patterns of the condensed grains showed no sharp peaks. It was found from IR absorption spectra that the particles contained C-H, Si-O, and Si-C bonds, irrespective of their initial abundances. These characteristics of the condensates were clearly different from those expected from equilibrium calculations.

Grain Formation Experiments by a Plasma Jet Apparatus

The observational fact that the interstellar and circumstellar dust grains are not crystalline but amorphous has been accumulated and it leads to the idea that the grain formation in space is a non-equilibrium phenomenon. In order to investigate the non-equilibrium condensation, we have developed a plasma jet apparatus. The high power of the apparatus enables to dissociate molecular sample gas completely and to obtain condensates from atomized gas. The purpose of our experiments is to examine the condensates from rapidly cooled atomized gas with various abundance ratios. In the experiments, we first focused on the condensation from mixtures of H, C, O, and Si atoms. Three kinds of gas mixtures, a mixture af H and C atoms, that of H, C, and Si atoms, and that of H, C, O, and Si atoms, were chosen as reactant condensable gases. Our experiments were executed with entirely new features: (1) condensation from atomized gas and (2) condensation from mixtures of silicon, oxygen, carbon and hydrogen atoms.

A Quenched Carbonaceous Composite (QCC) Grain Model for the Interstellar 220 Nm Extinction Hump

The dependence of the wavelength of peak absorption of dust grains on the grain size is investigated analytically by using an oscillator model for the absorption band. The peak wavelength of a weak absorption band is much less sensitive to the grain size than that of a strong band. This is explained by the fact that the surface mode, which is excited in the strong absorption band, is not raised in the weak absorption band. A quenched carbonaceous composite (QCC) synthesized from hydrocarbon plasma is found to have a weak absorption band at 220 nm. The absorption peak wavelength of the QCC grains falls well in the range of 217 ± 7 nm even if the grain size runs from 5 to 100 nm. This is compatible with the observed constancy of the 220 nm hump (217 ± 5 nm). By contrast, the absorption peak of graphite grains, which have a strong band around 280 nm and have been investigated as candidates for the hump, is very sensitive to the grain size. A quite narrow range of the grain size is required to account for the observed 220 nm feature. A weak absorption model, such as the QCC grains, is suggested to be a more likely candidate for the 220 nm extinction hump than a strong absorption model, such as graphite grains.