IR Laser Control of the Clustering of CF 3 Br Molecules during the Gas-Dynamic Expansion of a CF 3 Br/Ar Mixture: Bromine Isotope Selectivity

The infrared (IR) laser radiation control of the clustering of CF3Br molecules during the gas-dynamic expansion of a CF3Br/Ar mixture at the exit from a nozzle is investigated. Prominence is given to studying the possibility of bromine-isotope-selective suppression of the clustering of CF3Br molecules due to their resonance vibrational excitation in the gas-dynamic expansion zone near the nozzle. A continuous CO2 laser is used in experiments to excite molecules and clusters in a beam, and a quadrupole mass spectrometer is used to detect them. The experimental setup and the experimental technique are described. The dependences of the efficiency of molecule clustering suppression on the exciting laser radiation parameters, the gas parameters (composition, pressure) above the nozzle, and the distance from the nozzle exit section to a molecule irradiation zone are obtained. Bromine-isotope-selective suppression of molecule clustering is shown to occur at the exit from the nozzle due to the resonance vibrational excitation of gas-dynamically cooled CF3Br molecules. When CF3Br/Ar mixtures are used at pressure ratios p(CF3Br): p(Ar) = 1: 10 and 1: 30, the enrichment of a cluster beam by bromine isotopes are Kenr(81Br) ≈ 1.18 ± 0.09 and 1.12 ± 0.07 during the 9R(30) laser line (1084.635 cm–1) irradiation of a jet. The clustering suppression selectivity is α ≈ 1.18 when the mixture at the pressure ratio p(CF3Br): p(Ar) = 1: 10 is used. These results suggest that the proposed method can selectively control the clustering of the molecules containing the heavy element isotopes that have a small isotope shift in IR absorption spectra (OsO4, WF6, UF6).