High-pressure photoacoustic calorimetry of chromium hexacarbonyl: Volumes of heptane displacement from chromium pentacarbonyl heptane

We have developed high-pressure photoacoustic calorimetry to determine the volume of reaction for organometallic compounds. This allows the calculation of reaction enthalpies from the photoacoustic data. The photoacoustic signal for chromium hexacarbonyl with acetonitrile in heptane was examined from near ambient pressure to 100 MPa. Two components of the signal were resolved at 10-20 mM acetonitrile. The fast component is attributed to CO displacement by heptane (\u3c10ns), while the slow component (∼1 μs) is attributed to the subsequent displacement of heptane by acetonitrile. The amplitude of both components were pressure dependent demonstrating that the volumes of each reaction made a significant contribution to the photoacoustic signal (-21 and 17 ml mol-1, respectively). The enthalpies of CO displacement by heptane are 28 kcal mol-1 and heptane displacement by acetonitrile is -22 kcal mol-1. Neglect of the volumes of reaction in the PAC experiments can lead to an error of 6 kcal mol-1. © 2000 Elsevier Science B.V. All rights reserved