VAPOR-PHASE SPECTRA AND THE PRESSURE-TEMPERATURE DEPENDENCE OF LONG-CHAIN CARBOXYLIC-ACIDS STUDIED BY A CO LASER AND THE PHOTOACOUSTIC HEAT-PIPE DETECTOR

A resonant photoacoustic heat-pipe (PAHP) cell was constructed and use d for spectral studies of four long-chain saturated fatty acids (C10:0 to C16:0) at CO laser wavelengths and temperatures above that of the ambient. Vapor-phase absorption spectra were recorded at temperatures of 383 K for capric acid C10H20O2, 400 K for lauric acid C12H24O2 438 K for myristic acid C14H28O2, and 445.5 K for palmitic acid C16H32O2, respectively. In addition, the temperature dependence (298 to 393 K) o f vapor pressure was determined for C10:0; measurable PA signals were obtained at a temperature only a few degrees above the melting point f or this acid. The data observed for C10:0 could be linearly fitted fro m as low as 323 K, indicating the validity of the Clausius-Clapeyron e quation for temperatures lower than the 398 K < T < 541.4 K range anti cipated so far.