Modeling internal energy distributions in ion clusters: Comparison betweenexperiment and simulations

The internal energy distribution of Na+(CH3OH)(1-8) cluster ions has been e valuated by comparing experimental unimolecular rate constants measured in a triple quadrupole spectrometer to an RRKM rate analysis developed within the evaporative ensemble formalism. The significant ion-solvent binding ene rgies give rise to broad distributions, particularly for the smallest clust er ions. The role of internal energy on the number and type of cluster ion structures was then assessed by using Monte Carlo simulation methods. Predi cted onsets of hydrogen bond formation and the number of hydrogen-bonded O- H stretching bands in Na+(CH3OH)(1-7) were found to agree with previous vib rational spectroscopy experiments. The methodology introduced here can be u sed to estimate the internal energy content of any cluster that undergoes u nimolecular dissociation utilizing experimental or theoretical values for p roperties such as binding energies and vibrational frequencies.