A molecular beam study of water-methanol clusters

Clusters generated by injecting vapor from water-methanol liquid mixtures o f varying compositions through a pulsed valve, have been analyzed using a t ime-of-flight mass spectrometer. Neat clusters of water and methanol as wel l as mixed species have been observed, the relative populations varying wit h composition. The mole fractions in the vapor deviate significantly from t he values calculated assuming ideality of the liquid except at water mole f raction of 0.67, the composition around which the excess enthalpy is minimu m. An anomaly observed in the cluster populations at this composition is re lated to an extended hydrogen bonded interaction of molecules in the liquid . (C) 2001 Elsevier Science B.V. All rights reserved.