Time‐of‐flight mass spectrometry was used to measure the cluster size and distribution in photo‐ and electron‐impact ionized pure vapor expansions. In addition, fluorescence excitation spectroscopy measurements were made on the expansion of tellurium to determine the degree of cooling and identify the dominant cooling mode. Mass spectra were taken as a function of nozzle diameter, ranging from 0.2 to 13 mm, and source vapor pressure up to 400 Torr. Cluster size measurements were made on the following materials of moderately low and high melting point: Te, Zn, Se, Mg, Al, Ge, and Ag. Modeling of the dye laser excitation spectra of the Te dimer indicates that the vapor is rotationally cooled down to 150 K for a source pressure of 140 Torr, corresponding to a source temperature of 1073 K. Vibrational temperatures are significantly higher than rotational temperatures for all source conditions. All spectra obtained show only small clusters (<10 atoms per cluster) which are present in the source vapor before expansion. We conclude that a pure vapor source under the expansion conditions investigated does not produce measureable quantities of large clusters.