Strong Increase in the Efficiency of Isotope-Selective Infrared Laser Dissociation of Molecules under Nonequilibrium The
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ND LASER PHYSICS
Strong Increase in the Efficiency of Isotope-Selective Infrared Laser Dissociation of Molecules under Nonequilibrium Thermodynamic Conditions in a Shock Wave by Means of the Use of a Mixture with a Resonantly Absorbing Gas G. N. Makarova, * and A. N. Petina a
Institute of Spectroscopy, Russian Academy of Sciences, Troitsk, Moscow, 108840 Russia *e-mail: [email protected] Received July 7, 2020; revised July 7, 2020; accepted July 8, 2020
A strong increase in the efficiency of isotope-selective infrared laser dissociation of molecules (by an example of CF2HCl) under nonequilibrium thermodynamic conditions in a shock wave has been reached by using a mixture with a resonantly absorbed gas (CF3Br). It has been shown that the dissociation yield of CF2HCl molecules irradiated in a mixture with CF3Br molecules is more than a factor of 5–10 higher than the dissociation yield in the case of their irradiation in the form of pure gas. The dissociation threshold of CF2HCl molecules in the mixture with CF3Br molecules also decreases significantly from ≈1.5–2.0 to 0.2–0.3 J/cm2). This allows the efficient isotope-selective infrared dissociation of molecules at low exciting energy densities (Φ ≤ 1.0 −1.5 J/cm2), as well and increasing the selectivity of the process. The method has been described and the first results have been presented. The dissociation of CF2HCl molecules selective in the 35Cl and 37Cl isotopes with the enrichment factor K enr (35Cl /37 Cl) = 0.90 ± 0.05 is implemented when a CF2HCl/CF3Br = 1/1 mixture is irradiated by the 9R(30) (1084.635 cm–1) line of a CO2-laser at an energy density of Φ ≈ 1.3 J/cm2. DOI: 10.1134/S0021364020160079
1. INTRODUCTION Numerous studies using molecular and cluster beams are currently performed to develop low-energy methods for molecular laser isotope separation [1– 15]. The main goal of these studies is to find efficient and cost-effective methods for separating isotopes of uranium and other elements. The method of infrared multiphoton dissociation of molecules [16] was successfully applied in practice to separate carbon isotopes using CF2HCl molecules [17, p. 460]. The application of this method to separate isotopes of heavy elements is hindered by the high energy cost of the process (the dissociation of the UF6 molecule requires the absorption of about 40–50 infrared photons with a wavelength of 16 μm, i.e., an energy of 3.2–4.0 eV), the lack of efficient and high-power laser systems, and a number of other factors. Therefore, the development of low-energy molecular laser isotope separation methods, as well as alternative methods, is important and timely. As shown in [1, 18], an alternative to the lowenergy molecular laser isotope separation methods can be an approach involving isotope-selective infrared dissociation of molecules in a pulsed gas-dynami-
cally cooled molecular beam interacting with a solid surface, in particular, in a shock wave formed in front of the surface exposed to the intense molecular beam. In this approach, new thermodynamic condit
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