Isotope selective control over clustering of SF$_6$ molecules and dissociation of (SF$_{6}$)$_{m}$Ar$_{n}$ van der Waals clusters using an IR laser

We present the results of an investigation into the interaction of SF$_6$ 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 SF$_6$ 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 SF$_6$ molecules with a specific sulfur isotope by a CO$_2$ 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 $^{32}$S и $^{34}$S sulfur isotopes. In the case in which the clustering of SF$_6$ molecules was selectively suppressed, selectivity values $\alpha\ge$ 25–30 have been obtained. Upon selective dissociation of (SF$_6$)$_2$ dimers under similar expansion conditions of the gas mixture, selectivity values $\alpha\ge$ 20–25 for $^{32}$SF$_{6}{}^{32}$SF$_{6}$ dimers with respect to $^{34}$SF$_{6}{}^{32}$SF$_{6}$ dimers have been obtained. Particular attention has been paid to measurements at a high dilution of SF$_6$ in argon under conditions of predominant formation of (SF$_{6}$)$_{m}$Ar$_{n}$ mixed clusters. The potential of using studied processes as a basis for the technology of the laser isotope separation are discussed.