EVIDENCE FOR THE FORMATION OF CLATHRATE STRUCTURES OF PROTONATED WATER-METHANOL CLUSTERS AT THERMAL-ENERGY

Gas phase ion-molecule reactions of large protonated water clusters with methanol are studied in a flow reactor under thermal conditions. A distinct feature at H+(H2O)(21) corresponding to a stable clathrate structure is observed. Upon the addition of methanol from a reactant gas inlet, products of the general form H+(H2O)(n)(CH3OH)(m) (m = 1-5);are detected. Distinct features at n+m = 21. are observed under different experimental conditions, which are indicative of the formation of clathrate-like structures for mixed water-methanol cluster ions. A switching-reaction mechanism rather than an association is found to be operative. Considering the results-of the present study and those from previous molecular beam experiments suggests that clathrate structures arise from their inherent stabilities rather than due to kinetic effects.