Isotope Selective Control over Clustering of SF₆ Molecules and Dissociation of (SF₆)_mAr_n van der Waals Clusters Using an IR Laser

Abstract

We present the results of an investigation into the interaction of SF₆ molecules and clusters in a molecular beam with resonant IR laser radiation at different stages of the beam evolution along the axis of its propagation. The beam has been formed as a result of gas-dynamic expansion of a mixture of SF₆ with argon carrier gas during expansion from a pulsed nozzle. The experimental setup and the investigation method are described. It has been shown that selective vibrational excitation of SF₆ molecules with a specific sulfur isotope by a CO₂ laser near the nozzle edge causes suppression of the clustering process of these isotopic molecules. Selective IR excitation of clusters under the conditions of the formed cluster beam leads to isotopically selective dissociation of clusters. Depending on the experimental conditions including different distances of the irradiation zone of particles from the nozzle edge, the results of measuring the efficiency and selectivity of molecular clustering suppression and cluster dissociation processes are presented. It has been shown that both of these processes make it possible to achieve high selectivity values for the ³²S and ³⁴S sulfur isotopes. In the case in which the clustering of SF₆ molecules was selectively suppressed, selectivity values α ≥ 25–30 have been obtained. Upon selective dissociation of (SF₆)₂ dimers under similar expansion conditions of the gas mixture, selectivity values α ≥ 20–25 for ³²SF₆³²SF₆ dimers with respect to ³⁴SF₆³²SF₆ dimers have been obtained. Particular attention has been paid to measurements at a high dilution of SF₆ in argon under conditions of predominant formation of (SF₆)_mAr_n mixed clusters. The potential of using studied processes as a basis for the technology of the laser isotope separation are discussed.