Studies of molecular association in H2O and D2O vapors by measurement of thermal conductivity

The thermal conductivities of H2O and D2O vapors were measured in a modified thick hot wire cell between 358 and 386 K at pressures ranging from 100 to 1000 Torr. Analysis of the data indicates that molecular association to form a dimeric species is the main source of enhancement of the thermal conductivity of both vapors. The enthalpy and entropy of association of the H2O dimer are −3.59 kcal mol−1 and −18.59 cal deg−1 mol−1, respectively. The enthalpy and entropy of association of the D2O dimer are −3.66 kcal mol−1 and −18.67 cal deg−1 mol−1, respectively. The measured enthalpy of association of the H2O dimer is in agreement with recently reported ab initio molecular orbital calculations on the H2O dimer. The entropies of association of the H2O and D2O dimers are calculated theoretically and are found to be in agreement with the measured values.