Abstract

Helium clusters containing a few thousand monomers, formed from a sonic nozzle at 15 K, are doped with SF₆ molecules that they pick up in a scattering box containing this gas at partial pressures of 10⁻⁵ to 10⁻⁴ Torr. The IR spectrum of the doped clusters is obtained by line tunable CO₂ laser excitation of the SF₆ and bolometric detection of the photoevaporated helium atoms. If the clusters contain a single SF₆ molecule, the spectrum shows two absorptions located at 945.8 cm⁻¹ and 946.1 cm⁻¹, which indicates that the SF₆ molecule is located in an anisotropic environment, i.e., near the surface of the cluster. If the cluster contains two SF₆ molecules, the spectrum of the SF₆ dimer is recovered and found to be very narrow, as appropriate to the very low temperature of the medium in which the spectrum is taken (~0.4 K). The linear and quadratic dependence of the spectral intensities of, respectively, the monomer and the dimer features allows for an independent confirmation of the average cluster size.

© 1992 Optical Society of America