Determining the translational and internal temperatures of isolated metal clusters: A comprehensive approach based on molecular-beam-deflection experiments

An approach to translational, rotational, and vibrational temperatures of small metal clusters (GaMSnN, M = 0,1 and N = 6-16) in a molecular beam from a cryogenically cooled laser vaporization source is presented. The velocity distribution in the molecular beam is measured with a mechanical shutter at a fixed photoionization delay which gives an estimate of the lower bound of the translational temperature T-rans. These values of T-rans are found to be considerably smaller than the corresponding nozzle temperatures T-nozzie = 16-300 K. The rotational temperature T-rot is estimated from the comparison of an electric deflection experiment with molecular dynamics simulations and from magnetic deflection experiments to be in the range T-rot = 5-20 K for T-nozzie = 16 K. The vibrational temperature T-V1D is studied by comparing magnetic deflection experiments with a microscopic model based on avoided level crossings between vibrational, rotational, and Zeeman energy levels. For T(nozzie )50 K, Tvib Tnozzie is observed, while for lower temperatures, T-V1D > T-nozzle. Thus, T-rans T-or < T-V1D is found at least for N = 11,12 and the lowest nozzle temperature of 16 K.