furnace, i.e., in a zone where the temperature is substantially lower than inside. The apparatus is then put under vacuum mmHg) and subsequently flushed with argon. Importantly, the vacuum must then be restored and the pressure kept down to lo-' mmHg of argon before the vessel is introduced into the furnace (Thermolyne, type 21 100). The furnace is installed on top of a marble table equipped with anti-vibration feet. The temperature is then gradually raised from room temperature to 300°C within 15 min, while the tube is still kept evacuated to remove decomposition gases. The temperature is monitored with the help of a chromel-alumel (K-type) thermocouple and a Digi-Sense (Cole-Parmer) temperature controller. The whole assembly is left untouched for 24 h, after which the vessel is pulled out of the furnace and cooled down.
a-8T crystals are found on the lower rim of the hilt collector as well as on the inner wall of the glass tube, where they form a 2 cm wide deep-red ring located 2-4 cm below the exit of the furnace. Surprisingly, three other colored rings of micro-crystals are found above a-8T, i.e., in the outer part of the tube, which we identified as a-6T (orange), (1-4T (yellow), and a-3T (blue luminescence) from the bottom up. These lower oligomers are probably produced by the thermal decomposition of a-8T and crystallize in the tube at levels corresponding to decreasing temperatures for decreasing molecular weights. Attempts to grow a-8T crystals at lower temperatures in the range 220-280°C and at slightly higher pressures (lo-'-IO'mmHg of argon) failed and led to the decomposition of a-8T.
The a-8T single crystals were observed with an optical microscope (Zeiss, STEM1 SV8) under cross-polarized white light (polarizers HOYA 48 mm). Micrographs were taken at a magnification of 45.
X-ray analysis:
A careful examination of an aggregate stack of razor-bladethin orange crystals was made in order to select a suitable one for X-ray study. Several crystals were discarded because of close association or twinning. Finally, a very thin plate (0.04 x 0.5 x 0.8 mm3) was chosen in spite of an inappropriate shape for absorption effects. Data collection was carried out on an Enraf-Nonius Cad4 in front of a rotating anode Enraf-FR571 using CuKa radiation (40 kV, 70 mA). 5506 reflections were measured in the range 2.0" < 20 < 129.9", with h, k, and I such that -68 < h < 69, 0 < k < 9, and 0 < I < 6. This yielded 1925 unique reflections of which 1639 had I > 3 4 0 . The structure was solved by direct methods using SIR88 [33] and refined with CRYSTALS [34]. The structure was refined isotropically to 13 % when the DIFABS absorption correction [35] was applied to the uncorrected data. Anisotropic refinement converged at R = 6.59 and wR = 7.51 %, S = 1.142, and the maximum and minimum heights in final difference Fourier synthesis were 0.496 and -0.479 e k ' . Extinction correction was applied. An attempt at a weighting scheme did not give a suitable result. Atomic scattering factors were taken from the International Tables for X-Roy Crystallography [36].