Abstract
Mass spectrometric determinations have been made of size distributions of cluster ions produced by expansion of ionized mixtures of water and various carrier gases. Measurements span a range up to mass to charge ratios of 59 000. Dilute water–nitrogen carrier gas mixtures producing cluster masses up to 12 000 gave size distributions which are first order in water concentration. This observation is explained by the relatively large value of the ion–dipole associative collision cross sections which determined the rate of growth of cluster ions in the mass range studied. Studies in different mass carrier gases show that cluster ion size distributions are largely determined by the cross section for, and number of, associative collisions taking place during the expansion process. Estimates of associative collision efficiency have been made for water and alcohol cluster ion growth on expansion. Evidence has been obtained for steric inhibition of efficient alcohol collision processes compared to relatively efficient waterclustering.