A resonant photoacoustic heat-pipe (PAHP) cell was constructed and used 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 C<sub>10</sub>H<sub>20</sub>O<sub>29</sub> 400 K for lauric acid C<sub>12</sub>H<sub>24</sub>O<sub>29</sub> 438 K for myristic acid C<sub>14</sub>H<sub>28</sub>O<sub>29</sub> and 445.5 K for palmitic acid C<sub>16</sub>H<sub>32</sub>O<sub>29</sub> respectively. In addition, the temperature dependence (298 to 393 K) of vapor pressure was determined for C10:0; measurable PA signals were obtained at a temperature only a few degrees above the melting point for this acid. The data observed for C10:0 could be linearly fitted from as low as 323 K, indicating the validity of the Clausius-Clapeyron equation for temperatures lower than the 398 K < T < 541.4 K range anticipated so far.
Henk Jalink, Dane Bicanic, Mladen Franko, and Zoltán Bozóki, "Vapor-Phase Spectra and the Pressure-Temperature Dependence of Long-Chain Carboxylic Acids Studied by a CO Laser and the Photoacoustic Heat-Pipe Detector," Appl. Spectrosc. 49, 994-999 (1995)