Modeling Internal Energy Distributions in Ion Clusters:  Comparison between Experiment and Simulations

The internal energy distribution of Na + (CH 3 OH) 1 - 8 cluster ions has been evaluated 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 energies give rise to broad distributions, particularly for the smallest cluster ions. The role of internal energy on the number and type of cluster ion structures was then assessed by using Monte Carlo simulation methods. Predicted onsets of hydrogen bond formation and the number of hydrogen-bonded O−H stretching bands in Na + (CH 3 OH) 1 - 7 were found to agree with previous vibrational spectroscopy experiments. The methodology introduced here can be used to estimate the internal energy content of any cluster that undergoes unimolecular dissociation utilizing experimental or theoretical values for properties such as binding energies and vibrational frequencies.