ROTATIONALLY RESOLVED SPECTROSCOPY OF SF6 IN LIQUID-HELIUM CLUSTERS -A MOLECULAR PROBE OF CLUSTER TEMPERATURE

A rotationally resolved infrared spectrum has been obtained for SF6 mo lecules captured inside of helium clusters of approximately 4000 atoms . The spectrum is interpreted in terms of a spherical top Hamiltonian, although the resulting rotational constant is considerably smaller th an that of free SF6. This can be attributed to the interaction between the molecule and the surrounding helium liquid. The results indicate that the SF6 is located inside the helium cluster and a fit to the spe ctrum yields a rotational temperatures for the perturbed SF6 of 0.37 /- 0.05 K.