The exchange of H, D, and T atoms between water and dissolved hydrogen has been studied in both heavy and light water solutions. Values of the "exchange yield", Gtracer, for the isotopic hydrogen atoms have been deduced and are identified with the yield of D atoms from HDO in H2O, H atoms from HDO in D2O, T atoms from HTO in H2O and from DTO in D2O. These values are correlated by assuming that the medium, H2O or D2O, affects the total probability of dissociation of the tracer molecule (HDO, HTO, DTO) and that in HDO H atoms are more readily dissociated than D atoms.
The yield of Dz formed by a unimolec~~lar process in the y-ray irradiation of cyclohexane-dl? has been deduced from the isotopic composition of hydrogen evolved from C G H~~-C~D~~ mixtures. A value of 0.25 molecule/100 ev is found for this molecular" yield. This y~e l d is only slightly reduced by iodine but is considerably reduced in the presence of biphenyl.is the principal gaseous product formed in the fast-electron irradiation of cyclohexane, its initial yield being 5.5-5.8 molecules/100 ev. This yield is quite sharply reduced by snlall additions of solutes. Solutions containing -5 X moles/liter iodine, for instance, haveG(1-I?) , -4.0 (1); solutions of cyclohexane with benzene (1, 2), biphenyl, and terphenyls (3,4) show a similar behavior. From a study of curves of G(I-12) vs. iodine concentration, Burton et al. ( I ) conclude t h a t hydrogen is produced by two mechanisms each with a yield of 2 to 3 molecules/100 ev, one of which is lllore rapidly suppressed by iodine than the other. Studies of G(1-12) in biphenyl solutions lead to a similar conclusioll (3,4).The two mechanisms could be (a) a binlolecular mechanism involving hydrogen-atom abstraction from the parent lllolecule and (b) a unilnolecular mechanism in which ~nolec-ular hydrogen is split off in one step from an excited parent molecule. These two types of ~nechanisrns are sometimes referred to as "radical and molecular" or "intermolecular and intramolecular".The existence of two such processes has been demonstrated by Dewhurst (5) in the radiolytic decomposition of 72-hexane. high probability of "molecular" processes in organic lnolecules is shown by Dorflllan's work on the gas-phase radiolysis of ethane (6) where it was shown that 66% of the molecular hydrogen is formed by a molecular detachment process not involving free hydrogen atoms.By exan~ining the variation of the D ? yield in C G D I~-C G H~? mixtures we have determined the value of the 'uni~nolecular' yield of D2 from CGDls Its value is low, G(D2) (unimolecular) being 0.25 n~olecule/lOO ev.
The isotopic composition of hydrogen evolved in the radiolysis of C B D~T C B H~P mixtures has been measured in the presence of various amounts of benzene and iodine. The yield of the uni~nolecular decomposition and the specihc yield of the bimolecular reaction are reduced in approxin~ately the same proportion as the yield of total hydrogen. I t is concluded that (i) iodine and benzene interact to a comparable extent with both ~~nimolecular and bimolecular decon~position modes, (ii) it is probable that neither of these additives act by scavenging, and (iii) it is probable that they act by quenching a common precursor of the two decomposition modes. INTRODUCTIONWe have shown from measurements of the isotopic composition of hydrogen produced in the radiolysis of C6D12-C6H12 ~~l i x t u r e s(1) that part of the hydrogen is formed in a bimolecular processS n + C G I I~V -+ 1-12 + P PI where the atoms in the H z molecule come fro111 two different cyclohexane molecules, and part is formed in a unimolecular process CGH12 ---3 t I ? + P yield Gl(H)[ 3 I where both hydrogen atoms come from the same cyclohexane molecule. The symbol P represents any product or residue and XE is the reactive intermediate in the biinolecular process.The specific yield of the cleco~~~positionin a large excess of CGI-112 WilS show~l to be 0.25 molecules/100 ev absorbed in the C6DlZ. However, the yield of reaction [3] in pure CGI-112 may amount t o between 25% (2) and nearly 50% (3) of the total yield. I t is conceivable that this large "isotope effect" expresses variations in Gl(D) and Gl(H) with the isotopic con~position of the solvent due to some type of energy transfer or charge transfer effect. In the experinients described in this paper we used the yield of D2 fro111 CGDlZ as an "i~ldicator" of the efficiency of unimolecular processes in benzene and iodine solutions in cyclohexane. We also showed (1) that Gl(D), the yield of reaction [4], was reduced by biphenyl, and slightly reduced by iodine. We concluded that biphenyl could act as a quenchi~lg agent2 on the excited precursors involved in the unilllolecular decomposition.In this paper we describe a series of measurements of the isotopic composition of hydrogen evolved in the radiolysis of CGD12-C61-112 mixtures in the presence of varying amounts of benzene and iodine. We find that, for both these substances, G1(D) is reduced in approxi~llately the same proportioil as the total hydrogen yield, and we infer that the ~~nimolecular and bimolecular decolllpositio~ls are quenched t o approxilllately the salne extent by these substances. Burton and Chang (4)
We have measured the isotopic coniposition of radiolytic hydrogen evolved from mixtures of be~izene and cyclohexa~ie with their deuterated analogues. The data are interpreted in terms of first-order processes of the kinetic form (for C G D~? ) C G D I~ -, CGDlo + D: and secondorder processes CGDI? + S n + R, SD + C G H l j H D + I?.i\ complete kinetic analysis for the system CGDG-CGIIG has been ~n a d e from measurements a t the two ends of tlie concentration range. This gives a satisfactory prediction of tlie isotopic composition of hydrogen evolved from a n equiniolar CGHG-CGDG mixture. A first-order ) ield of D2 is fount1 in solutions of CGDI? in benzene which persists to 'zero' CGDI? corlcentration. The ~necha~iisms of the first-order process studied ill these experiments, and of tlie 'unscnvengeable' or 'molecular' yields of radiolytic hydrogen, are discussed.Studies (1-3) of the isotopic conzposition of hydrogen formed in the radiol~.sis of light and heavy hydrocarbons have shown the existence of tlvo radiolytic processes: a decomposition in which both hydrogen atoms in the H 2 ~llolecule colne from the same hj-drocarbon molecule, where the hydrogen atoms in the 1-12 molecule come from two hydrocarbon niolecules.We call the first 'the first-order process' since its existence is shown, in our esperinzents, by a yield of D? which is first order with respect to the c o~l c e~l t r a t i o~l of the deuterated 11) drocarbon. T h e second we call 'the seconcl-order process' since the j~ielcl of D: forllled by it has a second-order dependence on the concentration of the deutelatecl 11) clrocarbon.T h e yield ol the first-order process is calculated ~v i t h the assumption that the amount of energy absorbed by the deuterated hydrocarbon is proportional to its mole fraction in the mixture. W e have previously called the first-and seconcl-order yields the 'unimolecular' and 'bimolecular' yields. T h e new terminology emphasizes the operational definition and avoids conlus~on in discussion.In reference 3 ~v e have described esperime~its on hydrocarbon mixtures in ~vhich the variation of the first-order yield with solvent clemonstrates that the energy absorbeel by the deuterated l~j~drocarbon is not deternzinecl simply by its nlole fraction. T h e major part of this paper is concerned with ~nivtures of heavy anel light benzene in \vhich the deviations from the mixture law as clescribed in reference 3 appear to be absent. Experi~n e n t s on other mixtures of benzene and cyclohexane, variously deuterated, are also described.
The distribution of plutonium between neutron-irradiated uranium and some rare earth metals has been examined as a function of temperature in the range 1160° to 1350 °C. The results are used to calculate [Formula: see text] the limiting partial molal heat content of plutonium, at 1250 °C. in lanthanum, cerium, neodymium, and a commercial preparation of mixed rare earths (misch metal). The following values (in kilocalories) were obtained: lanthanum 2.9, cerium 1.1, neodymium 0.0, and misch metal 1.1. The maximum error associated with these values is ±0.4 kilocalories.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.