Kinetics and energetics of hydrogen bond dissociation in isolated acetic acid-d1 and -d4 and trifluoroactic acid dimers

A quantitative determination of the rate constant, activation energy, entropy, and enthalpy of dissociation of hydrogen bonds in deuterated acetic acid-d1, -d4, and trifluoroacetic acid dimers in the gas phase was performed by resonant CO2 laser photoacoustic spectroscopy. Within the experimental error, the kinetics and energetics of hydrogen bond dissociation were found to be independent of deuterium substitution of the hydroxy-hydrogen for pressures below 100 mbar. On the other hand, the dynamics, but not the energetics, of H bond dissociation are affected by the chemical nature of the rest group R (e.g., CH3, CD3, or CF3) of the carboxylic acid.