DIRECT TEMPERATURE-MEASUREMENT IN ALKALI-HALIDE CLUSTER BEAM

The temperature of a sodium fluoride cluster beam produced by laser va porization is estimated from the rotationally-resolved laser spectrosc opy of the Na-2 dimer. The cluster beam is obtained by laser vaporizat ion of a sodium rod in a mixture of helium containing a small amount ( 1%) of SF6. Both rotational and vibrational temperatures (respectively 170 K and 400 K) are much higher than expected from a simple theoreti cal model of a supersonic beam. These temperatures can be lowered to 7 0 K and 250 K respectively by cooling the nozzle to liquid nitrogen te mperature.