Pulsed supersonic source producing clusters with an adjustable vibrational temperature

We report the construction and operation of a novel cluster source that produces clusters with well-defined vibrational temperatures. Clusters seeded in He gas are thermalized in a cavity before undergoing a weak supersonic expansion. This weak expansion does not affect their vibrational temperature. An optimized source design ensures a high cluster density in the beam. The vibrational temperature is measured by studying the magnetic deflection of superparamagnetic clusters. We show that thermal equilibrium with the source temperature is achieved for long residence times of the clusters in the cavity. A closed-cycle helium refrigerator coupled to the source body controls the source temperature. Under these conditions, cluster vibrational temperatures from 58 to 300 K are currently obtained.