AB-INITIO CALCULATIONS OF HYDROGEN-BONDED CARBOXYLIC-ACID CLUSTER SYSTEMS - DIMER EVAPORATIONS

Ab initio calculations were performed on proton bound formic acid and acetic acid dusters, (RCOOHH+ at various levels of theory. Three types of competitive structures were deduced: Open-chain structures are fav ored energetically for lower members (n less than or equal to 5) of th e duster series, chains terminated with a cyclic dimer unit at one end for intermediate n and chains terminated by cyclic dimer units at bot h ends are favored for high n (n greater than or equal to 6). The comp utational results corroborate previously reported experimental results from this laboratory, according to which there is a changeover from m onomer evaporation from clusters of low n to dimer evaporation at n gr eater than or equal to 6 for R = H. Fairly good agreement was obtained between calculated and experimental binding energies.