¹³C and ^33,34S isotope effects on the vapour pressure of liquid carbon disulfide

Abstract

. Can. J. Chem. 54, 3007 (1976). Precision isotope ratio mass spectrometry has been used to determine the relative vapour pressures of the four principal isotopic species of liquid carbon disulfide. Relative to the principal species '2C32S3'S = 1.000000. Introduction For a long time it was believed that substitution of a heavier isotope for a lighter isotope in pure polyatomic molecular liquids invariably decreased the vapour pressure of the liquid. This relation between the vapour pressure and molecular weight is usually described as a normal vapour pressure isotope effect (1). While many molecular systems do indeed display normal vapour pressure isotope effects ( H 2 0 and D 2 0 provide perhaps the best known example), other systems are known which show an inverse isotope effect, i.e., the heavier species has the higher vapour pressure. For example, it is well established that the vapour pressure of 13CH30H is greater than that of 12CH301-I (2). For some systems, both kinds of effects have been observed for a given element, with the isotope effect changing sign when the temperature is changed. The deutero-rnethanes are an example of this class (3). Perhaps even more unexpectedly, systems are also known for which an inverse isotope effect is produced by substitution in one part of a polyatomic molecule, and a normal isotope effect by substitution in another part of the same molecule (2, 4, 5).

13C and 33,34S isotope effects on the vapor pressure of liquid carbon disulfide

“…1 where they are compared with the data points reported by Betts and Buchannon (7). The temperature dependence of the calculated effects is evident and in our opinion the calculations are in satisfactory agreement with the experimental data.…”

“…We have estimated the correction terms from available data 011 the virial coefficient (8) and molar volume (9) (neglecting the isotope effects on these parameters) and find them negligible in comparison with the experimental error (7). The reduced partition function ratio is then well approximated by the vapor pressure ratio.…”

Carbon kinetic isotope effects in the oxidation of oxalate by permanganate in aqueous solutions of sulfuric acid

“…These conclusions have led us to examine 12C/ 13C fractionation for other processes, involving decomposition of oxalate to C02, for which one may reasonably expect C-C bond rupture not to be rate-determining. In a subsequent publication, we describe such a process, involving photolysis of the Fe(II1)-oxalate complex in aqueous solution (9).…”

The dependence on wavelength of 13C isotope effects in photolysis of aqueous solutions of ferrie oxalate

“…Sufficient of this compound was dissolved in 0.25 M to give a solution 0.012 M Fe(II1). Air-free solutions were exposed to light of the desired wavelength, and the C02 produced was collected by vacuum transfer, dried, purified, and its isotopic composition determined as described previously (5). In each case less than 17, decomposition of the oxalate occurred, so that no correction was made for possible changes in the isotopic composition of the remaining material.…”

“…Our interest in these processes arises from a recent study of 13C isotope effects in the chemical oxidation of oxalate to C 0 2 by aqueous KMn04 (5). It occurred to us, as a result of speculations about the mechanism described in ( 9 , that a rate-controlling step which led ultimately to decomposition of oxalate, but which did not involve C-C bond breakage, might well be expected to show a small or even zero 13C isotope effect.…”