Investigations of protonated and deprotonated water clusters using a low-temperature 22-pole ion trap

A new tandem mass spectrometer, containing a temperature-variable 22-pole ion trap, has been constructed. It is applied, as a first application, to kinetic and spectroscopic investigation of charged water clusters produced from a supersonic expansion. Using low-pressure He or H-2 as buffer gas for collisional thermalization, refrigeration of the ion trap allows a good control of the cluster temperature over the range 77-350 K. It provides an accurate means of determining the dissociation energies of both protonated and deprotonated water cluster ions [HI(H2O)(n) and OH-(H2O)(m)] by measuring the dissociation rates at various temperatures along with their internal energies calculated from vibrational frequencies provided by density functional theory calculations. In this report, results of the thermochemical measurements for H+(H2O)(4-10) and OH-(H2O)(3-7) at well-defined cluster temperatures are presented. The feasibility of using this ion trap to acquire temperature-dependent infrared spectra of charged water clusters is also demonstrated with H+(H2O)(6).