Specific heat capacities at constant volume (c v ) of water, methanol, and their mixtures were measured with a new adiabatic calorimeter. Temperatures ranged from 300 K to 400 K, and pressures ranged to 20 MPa. Densities were determined at the initial and final end points during each calorimetric experiment. The calorimeter is a twin-cell type whose sample and reference cells (33 cm 3 ) and their shields are heated by electric power. The cells are surrounded by a high vacuum. During the experiment, the heating power was carefully controlled so that the cell temperature increased uniformly. The reference cell was always evacuated and was heated with a constant current. The temperature of the sample cell tracked that of the reference cell temperature by means an automatic control system. Automated sample pressure measurements were made with a crystal quartz transducer. The expanded relative uncertainty for c v is estimated to be 1% for liquid-phase measurements, and for density it is about 0.2%.
To investigate the photodecomposition mechanism of poly(di-n-hexylsilane) (PDHS), the ultraviolet (UV) light irradiation time dependence of the optical absorption (OA) and the piezoelectric photothermal (PPT) signals were measured in vacuum. A strong OA peak at 370 nm and a broad OA band at approximately 320 nm related to the all-trans and helical conformations, respectively, were observed. With increasing UV light irradiation time, their intensities decreased and blue shifts were observed because of the decomposition of Si-Si bonds in the silicon backbone. In the PPT spectrum, a nonradiative recombination peak associated with the all-trans conformation was also observed at 370 nm. When UV light irradiated the sample, in addition to the decrease in the intensity and the blue shift of the PPT peak at 370 nm, new PPT signals at approximately 290 nm were observed. We concluded that these signals were caused by the silicon and/or carbon dangling bonds generated by photodecomposition in vacuum. #
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