Takatoshi Narisawa

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.

Vibronic analysis and symmetry of the lowest energy ultraviolet transition of thiophen

High resolution and temperature dependence measurements have been recorded for the lowest energy u.v transition of thiophen. Based on the new observations of the hot bands the vibronic fine structure has been reassigned. The new assignment can be fitted well to the spectra of deuteriated derivatives. The first band system of the u.v. spectrum is assigned to the ψ4â†�ψ3(B2) transition. This conclusion is supported by a comparison of the ionization potentials and transition energies of some five-membered heterocycles.

ON THE CARRIER OF THE EXTENDED RED EMISSION AND BLUE LUMINESCENCE

Filmy-QCC, an organic material synthesized in the laboratory, exhibits red photoluminescence (PL). The peak wavelength of the PL ranges from 650 to 690 nm, depending on the mass distribution of polycyclic aromatic hydrocarbon (PAH) molecules, and the emission profile is a good match for that of the extended red emission (ERE) in the Red Rectangle (RR) nebula. The quantum yield of the PL ranges from 0.009 to 0.04. When filmy-QCC is dissolved in cyclohexane, it exhibits blue PL in the wavelength range of 400-500 nm with a quantum yield of 0.12-0.16. The large width of the red PL and the large wavelength difference between the PL of the filmy-QCC as a solid film and in a solution indicate that there is a strong interaction between the components of filmy-QCC. The major components of filmy-QCC are PAHs up to 500 amu. Our laboratory data suggest that the blue luminescence observed in the RR nebula is probably caused by small PAHs in a gaseous state, and the ERE is caused by larger PAHs in dust grains.

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.

Excited States as a Probe of Structural Phase Transitions in Polyphenyl Crystals

Phase transitions in biphenyl and p-terphenyl crystals were studied by the laser induced fluorescence and the absorption spectroscopy. In biphenyl, besides the intrinsic band starting from a false zero-phonon peak at 302.5nm, an excimer-like broad band appeared at about 480nm. The fluorescence decay curve changes near T c =17K and 40K, since the fluctuations of tortional vibration near T c have an influence on the energy transfer rate from the intrinsic excited state to the excimer-like state. The deviation from the Urbach-rule below T 1 = 40K in the absorption tail of biphenyl is also attributed to the tortional amplitude mode. In p-terphenyl, unlike the biphenyl case, sharp absorption peaks to the tortional levels in the excited state appears up to 50K and the fluorescence intensities gradually change with temperature in a characteristic way.

Fluorescence Studies on Photo-Induced Structure Changes in Purified Biphenyl Crystals

Fluorescence spectra of pure biphenyl crystals were measured over a wide temperature range. In contrast to the sharp peaks near 530 nm observed in crystals grown from methyl alcohol solution, a new broad band around 500 nm was found in zone-refined crystals at 5.0 K when the intense exciting laser was employed. From the temperature dependent behavior and the fluorescence decay characters, it is suggested that the new excimer-like band is related to photo-induced structural deformation in biphenyl crystals.