Selenium isotopic fractionation during reduction to Se 0 and H 2 Se

Abstract

During reduction of [Formula: see text] to Se 0 by NH 2 OH • HCl, the selenium isotope selectivity fits a two step model with the second step two orders of magnitude faster than the first. The ratios of the isotopic rate constants, k 76 /k 82 , are 1.007 and 1.020 for the first and second steps, respectively. The corresponding k 76 /k 80 values are 1.004 6 , and 1.013 3 . During the reduction of [Formula: see text], to H 2 Se by a H 3 PO 2 –HI–HCl mixture, the H 2 Se was initially enriched but sporadically became depleted in the heavier isotopes as the reaction progressed. This is attributed to the formation of Se 0 as an intermediate and the subsequent reaction of its surface layers to produce H 2 Se.For all data, the relation δ 82 Se = (1.5 4 ± 0.02)δ 80 Se was observed as predicted theoretically.