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Ultrasonic absorption measurements are reported for gaseous CF3Cl, CF3Br, CHF2Cl, and CH3Cl between room temperature and the lower temperatures 163 K, 193 K, 198 K, and 213 K, respectively. Starting from a statistical point of view, the relaxation behavior is divided into three classes, which are associated with the positive, zero, and negative slope in a log(k) versus 1/T plot. On this basis the vibrational relaxation behavior of CF4, CF3Cl, CF3Br, CHF3, CHF2Cl, CH3Cl, NF3, PF3, and BF3 is discussed especially in the critical temperature to boiling point region. This temperature region is used as a reference for comparing different molecules.

A method is described which allows a single-pulse analysis of photoacoustic signals. Isotope specific excitation of D(2)S and HDS is performed with a TEA CO(2) laser, and the concentration change of the two species caused by H-D exchange after fast mixing of H(2)S and D(2)S is monitored. No influence of the laser radiation on the exchange reaction could be detected. Thus the progress of an independent chemical reaction was analyzed by a concentration measurement. The time resolutions is determined by the repetition rate of the laser.