MEASUREMENT OF VELOCITIES OF CLUSTERS GENERATED IN SUPERSONIC-FLOW

An apparatus is described for measuring the speeds of molecular cluste rs in a flight tube under conditions of gas density that would overwhe lm the system in conventional measurements of gas velocities. Although the apparatus incorporates no new design principles it is effective i n practice. It provides the information needed in timing the evolution of the extremely fast phase changes that occur in highly supercooled clusters. The state of clusters is monitored as a function of their di stance and, hence, time-of-flight along their path. Illustrative examp les of velocity measurements are given.