Efficient, highly selective laser isotope separation of carbon-13

Abstract

We recently demonstrated an original approach to highly selective laser isotope separation of carbon-13 that employs vibrational overtone pre-excitation of CF 3 H together with infrared multiphoton dissociation [O.V. Boyarkin, M. Kowalczyk, T.R. Rizzo, J. Chem. Phys. 118, 93 (2003)]. The practical implementation of this approach was complicated by the long absorption path length needed for the overtone excitation laser beam. In the present work, we employ a low overtone level for the pre-excitation that shortens this pathway, facilitating engineering of the process. We propose an optimal configuration of the isotope separation scheme and consider a realistic example of a separation unit for isotopic enrichment of carbon-13 to 94%-98%. The photon energy expenditure of 97 eV per separated atom is much lower than that of the current commercial laser technology, making this process economically feasible. While the use of infrared lasers for molecularbased separation of stable isotopes has led to many interesting findings and promising demonstrations [1][2][3][4][5][6][7], few laser isotope separation schemes have reached the stage of commercial application [8]. In the case of schemes based on infrared multiphoton excitation, the limitation is their low isotopic selectivity. Physical methods of isotope separation, such as low temperature distillation of CO in the case of carbon, do not alter the working molecule, and this facilitates the implementation of a multi-cycle separation process [9]. Although the selectivity of each cycle is low, the repetition of many separation cycles makes it possible to achieve the high levels of selectivity demanded by the market. Because molecular laser isotope separation techniques that are based on infrared multiphoton dissociation chemically convert the parent molecule into a new species, repetitive cycles can be complicated and costly. Development of a single-stage, energy-efficient, laser separation technique that could produce the high levels carbon-13 enrichment required by the market (above 95% or above 99%) would fill an important niche.u Fax: +41-21-693-5170, E-mail: Oleg.Boiarkin@epfl.chOver the last several years we have developed a highly selective separation scheme for carbon-13 that combines isotopically selective vibrational overtone pre-excitation (OP) of the CH-stretch vibration in 13 CF 3 H followed by selective IRMPD of the pre-excited molecules (Fig. 1) [10][11][12]. The CF 2 fragments combine via 3-body collisions to form C 2 F 4 , which can be separated from the starting material. We have demonstrated selectivities up to 9000 (99% enrichment in carbon-13 starting from CF 3 H in natural abundance) that can be enhanced at high sample pressure by V-V collisional relaxation [11]. Since our original discovery of this unexpected effect [11], we have taken several steps that significantly increase the yield of the process, bringing it closer to commercial relevance. In particular, overlapping the preexcitation laser pulse with a short (50 ns) dissociation pulse ...

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