Fractionation of dichloroisotopologues and 35Cl/37Cl isotopes in molecular effusion of dichloromethane

We have modeled the physical processes, which demonstrate chlorine isotope fractionation in molecular effusion of dichloromethane (DCM) (Graham' law of effusion scheme). Variations in the amounts of dichloroisotopologues in the pool of DCM effused from a volume with high DCM pressures (about 0.1-10.0 Pa) into that with low pressures (about 2 x 10(-7) Pa) through the membrane with six 3 mu m-holes were measured using mass spectra. The kinetic effusion isotope effects of Cl-35(2) or (ClCl)-Cl-35-Cl-37 isotopologues relative to Cl-37(2) isotopologue are a Raleigh-type simple first-order model of isotope fractionation. A quadratic equation has been proposed in which amounts of dichloroisotopologues in the DCM pool are coefficients, and its two solutions reflect the probabilities of revealing Cl-35 and Cl-37 by two positions of chlorine in the molecule. Virtual site-specific Cl-35 and Cl-37 isotope fractionation was detected: in the residual DCM pool, at one site of chlorine in the molecule, the probability of finding Cl-35 relative to Cl-37 increased; vice versa, at the other site it decreased. The observed features in Cl-35/Cl-37 abundance ratios in sites of molecules reflect the history of DCM pool formation: it can be determined in a pool of DCM that remained after partial effusion or a pool effused from an external source. (C) 2014 Elsevier B.V. All rights reserved.