Recoil Tritium Reactions Research Articles

Effect of γ-Ray Irradiation on the Recoil Tritium Reaction in Xenon–Hydrogen Mixtures at 77 and 4.2 K. Competition of the Tunneling Reaction with the Combination Reaction

Abstract Recoil T-atom reactions have been studied in Xe–H2–D2 mixtures at 77 and 4.2 K. When T atom reactions were caused at 77 K by neutron irradiation at an extremely low dose rate of γ-rays, a large isotope effect (kHT/kDT≈7) on the formation of HT and DT was observed. When T-atom reactions were caused at 77 K by neutron irradiation at a high dose rate of γ-rays, there was no isotope effect (kHT/kDT≈1) on the formation of HT and DT. The production of H and D atoms by γ-irradiation of the Xe–H2–D2 mixtures was studied by ESR spectroscopy at 4.2 K. The significant effect of the dose rate of γ-rays on the HT and DT formation was interpreted in terms of competition between a tunneling reaction of thermal T atoms with H2(D2) and a combination reaction of thermal T atoms with H(D) atoms produced by γ-radiolysis.

Recoil tritium reaction in solid hydrogen at ultralow temperatures

Reactions of recoil T atoms were studied in solid H 2 -D 2 mixtures at 4.2 K. The fraction of HT in the sum of HT and DT yields, [HT]/([HT]+[DT]), is roughly equal to the mole fraction of H 2 in the H 2 -D 2 mixtures. These yields were compared with the yields of H atoms produced by γ-radiolysis of the H 2 -D 2 mixtures at 4.2 K. From the comparison, it was concluded that formation of HT could not be due to combination of thermalized T atoms with hydrogen atoms from γ-radiolysis of solid hydrogen during reactor irradiation but must be due to hydrogen atom abstraction by recoil T atoms from H 2 and D 2

Recoil tritium reaction in rare gas-ethane solid mixtures at ultralow temperature

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRecoil tritium reaction in rare gas-ethane solid mixtures at ultralow temperatureKwang Pill Lee, Yoshiaki Ito, Yoshiteru Fujitani, Tetsuo Miyazaki, Kenji Fueki, Yasuyuki Aratono, Masakatsu Saeki, and Enzo TachikawaCite this: J. Phys. Chem. 1986, 90, 21, 5343–5347Publication Date (Print):October 1, 1986Publication History Published online1 May 2002Published inissue 1 October 1986https://doi.org/10.1021/j100412a089RIGHTS & PERMISSIONSArticle Views27Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (608 KB) Get e-Alerts

Radio-liquid chromatogrphy for tritium labelled organic compounds using CaF2/Eu/ scintillator

The radio-liquid chromatography for the tritium labelled compoounds was constructed with a CaF2/Eu/ scintillator and applied successfully to analyze the products of recoil tritium reactions with trans-stilbene. The detection efficiency of tritium of 0.8% and the lowest detectable activity of 60 nCi were obtained for a 100–150 mesh CaF2/Eu/ scintillator.

Reactions of recoil tritium atoms with toluene and benzonitrile.

Recoil tritium reactions in the aromatic ring were investigated with toluene and benzonitrile in the moderator-free and the C6F6-moderated systems in terms of the intramolecular tritium distribution, the relative tritiation rate, and the isotope effect in toluene. The reactions free from hexafluorobenzene are in essential agreement with non-selective nature shown in hot atom reactions. The addition of the moderator to the systems changes more markedly the uniform labeling to o,p-orientation in toluene than in benzonitrile, and the 1.17 PhCH3/PhCN tritiation rate (in PhCH3-d8/PhCN, 0.942) to the 1.89 PhCH3/PhCN one (in PhCH3-d8/PhCN, 1.51) when the mole ratio of C6F6/substrate is about 100. These findings agree with the electrophilic nature of the tritium at lower energies. The H/D isotope effect in the moderated system is given as 1.89/1.51 or 1.25 and is substantially the same as that (1.24) in the moderator-free system.

Moderator effects on recoil tritium reactions with lithium beta-phenylpropionate.

The recoil tritium reactions were studied with lithium beta-phenylpropionate having both the aromatic and aliphatic C-H bonds in the molecule, mainly in terms of the moderator effect on the intramolecular tritium distribution. Recoil tritium atoms were produced by the 6Li(n,alpha)3H reaction. Water molecules were used as the moderator. The tritium activity of the ethylene group represented relative to that of the corresponding ring assumed as a standard (= 100) is 30 in the moderator-free system and is reduced to 13 in the moderated system in which the H2O/beta-PhC2H4CO2Li mole ratio is 328. In the ring, the tritium distribution shows a slight ortho- and para-orientation in the moderator-free system and the selectivity is pronounced when the H2O/beta-PhC2H4CO2Li mole ratio is large. The data show that the aromatic ring tritiation in the moderated system is given by increasing contribution of the reactions of tritium atoms having lower energy than the threshold energy of the ethylene group tritiation.

The reactions of recoil tritium atoms with toluene in the C6F6-moderated systems.

The T-for-H substitution reaction was studied in the recoil tritium reactions with toluene in C6F6-moderated systems. The moderator-free control experiment showed an approximately uniform labeling in the aromatic ring, with a slightly enhanced reactivity in the ortho- and para-positions (o: 41%, m: 38%, p: 21%) and showed a preference for ring tritiation over methyl group tritiation (23 relative to the corresponding ring assumed as a standard (= 100)). The addition of hexafluorobenzene progressively changed the uniform distribution to a marked ortho- and para-orientation and decreased the relative tritium activity of the methyl group. If the C6F6/PhCH3 mole ratio is 204, the tritium distribution in the ring is o: 53%, m: 22%, p: 25% and the methyl group activity is reduced to 2. The data show the existence of the threshold energy of side chain tritiation and that the selective aromatic ring tritiation is given by increasing contribution of the reactions of tritium atoms having lower energy than the threshold energy.

Reactions of energetic tritium atoms with ethyl fluoride over an extensive pressure range

Recoil tritium reactions with ethyl fluoride have been studied over a pressure range of six orders of magnitude. The results show that subsequent to T-for-H substitution, the fraction of collisionally stabilized C2H4TF ranges from 0.05 at 10−2 Torr to 0.91 in the liquid. The low pressure results indicate that 95% of the C2H4TF molecules being formed possess an excitation energy of 65 kcal mol−1 or higher. The high pressure and liquid phase studies suggest that about 15% of the excited molecules have energies distributed in a very long and narrow tail at the high energy end.

Recoil tritium reactions with 1,2-difluoroethylenes

Recoil tritium reactions with cis- and trans-CHF=CHF have been studied. The results indicate that the majority of the tritium-labeled parent molecules are formed via the direct T-for-H substitution process and that the geometric isomers are formed via unimolecular isomerization of the excited parent molecules. On the other hand, the recoil tritium addition process will give rise to an excited radical that immediately converts to a bridged complex. Such a bridged complex may either isomerize to effect a net 1,2 F-atom migration to give CHT=CF/sub 2/ as the final product or expel an F-atom to form CHT=CHF.

Recoil tritium reactions with molecular hydrogen. Part 3.—Isotope effects

Scavenger and moderation studies on T + HD and T + H2/D2 mixtures in the presence of ICl scavenger and the moderators He, Ar and Kr are reported. Kinetic-theory analysis of the product yields leads to similar conclusions to those reported for the T + H2 and T + D2 systems. However, the isotope effects are found to depend on the nature of the moderator species, and the intermolecular isotope effect is found to be significantly smaller (ca. 1) than that determined from the separate, single-reactant systems, or that predicted from theoretical excitation functions.

Temperature effect on recoil tritium reactions in solid alkanes at 20-300 K. Comparison of recoil tritium atoms with hydrogen(deuterium) atoms in radiolysis

Hydrogen atom abstraction by recoil T atoms in neopentane and decane-d/sub 22/ has been studied at 20, 77, 195, and 300 K by means of ESR spectroscopy and radiogas chromatography. The results are compared with the reaction of H (or D) atoms produced by ..gamma.. radiolysis. When the experiments are conducted at 77 K, the reaction or recoil tritium atoms in the neo-C/sub 5/H/sub 12/-i-C/sub 4/H/sub 9/D (2 mol %) and n-C/sub 10/D/sub 22/-n-C/sub 10/H/sub 22/ (10 mol %) mixtures do not parallel those of H and D atoms generated by ..gamma.. irradiation, whereas the results at other temperatures below and above 77 K (20, 195, and 300 K) are more nealy comparable. The different results at 77 K are attributed to the ability of H and D atoms but not T atoms to diffuse and react with i-C/sub 4/H/sub 9/D (or n-C/sub 10/H/sub 22/) solute molecules. The failure of the thermal diffusion of the T atoms at 77 K is explained by a model in which nearly all of the recoil T atoms react either by hot reaction or have a high probability of reacting with a fragment near the end of the path and only a few percentmore » of them diffuse into the bulk matrix.« less

Recoil tritium reactions with molecular hydrogen. Part 2.—Moderation effects

Moderation studies of the T + H2 and T + D2 systems moderated by helium, argon and krypton are reported. The derived kinetic parameters indicate that helium is a much poorer moderator in these systems than is either argon or krypton. This observation is rationalised by considering the effect of collisional dissociation of translationally excited product in the different moderators, and the effect of an αHe, which declines as the collision energy increases.

Recoil tritium reactions at extremely low pressures

Recoil tritium reactions with cyclobutane and ethyl chloride have been extended to pressures as low as 5 × 10−2 torr. The results indicate that more than 85% of the excited molecules subsequent to T-for-H substitution have excitation energies higher than 2.6 eV.

Recoil tritium reactions with CH3SiD3: pressure dependent yields

The T + CH3SiD3 system has been studied to evaluate the effect of reactant pressure on parent-T yield. The substitution yields for C—H and Si—D bonds have been found to be in the ratio 1 : 1.7. The decomposition rate of the excited parent-T has been calculated on the basis of the above ratio and compared with experimental yields at low pressure. Hypotheses to explain the discrepancy between calculated and experimental values are discussed.

Analysis of the Products of Recoil Tritium Reaction with Limonene

Analysis of the Products of Recoil Tritium Reaction with Limonene

Recoil tritium reactions with tert-butyl chloride

Recoil tritium reactions with tert-butyl chloride

Recoil tritium reactions with methylcyclohexene. Test of the assumption of energy randomization prior to unimolecular decomposition

The reactions of recoil tritium atoms with the three methylcyclohexene isomers were studied in the gas phase at 135 deg C. T was produced by /sup 3/ He(n,p)T. Recoil tritium atom abstraction, addition, or T-for-H substitution reactions accounted for 90% of the gas-phase products. Following activation by T- for-H substitution, the unimolecular decomposition of 4-methylcyclohexene-t (to give propylene-t or butadiene-t) and the unimolecular decomposition of 3- methylcyclohexene-t (to give ethylene-t or 1,3- pentadiene-t) was established from the pressure dependence of the product yield in the 300-1200-torr pressure range. The apparent rate constants for these unimolecular decomposition processes were determined as 1 x 10/sup 7/ and 3 x 10/sup 6/ sec/sup -1/, respectivel y. The rate constants for the unimolecular decomposition of cyclohexene1-t and cyclohexene-3-t (formed by T-for-methyl substitution on 1- methylcyclohexene and 3-methylcyclohexene, respectively) were nearly equivalent. In addition, the average energy of excitation following T-for-methyl substitution is the same in cyclohexene-1-t and cyclohexene-3-t, namely, 6.0 to 6.5 cV. It was concluded that the RRKM (Rice, Ramsperger, Kassel, and Marcus) assumption of energy randomization prior to unimolecular decomposition is valid for the recoil tritium initiated unimolecular decomposition of cyclohexene. (44 references) (auth)

Recoil tritium reactions with cyclohexene and alkenes. Determination of rate parameters

Kinetic rate parameters can be determined from recoil tritium reaction studies although the energy distribution of the reacting tritium atoms is not known. T is produced by /sup 3/He(n,p)T. Recoil T-for-H substitution on cyclohexene gives excited cyclohexene-t molecules. The dependence of product yield on pressure (in the hexene-t molecules decomposed unimolecularly to give ethylene-t and butadiene-t with an apparent rate constant (at 135 deg ) of 5 x 10/ sup 6/ s/sup -1/. The s parameter in the RRK (Rice, Ramsperger, and Kassel) treatment of the unimolecular decomposition of cyclohexene was determined as s = 24. Similarly, the pressure dependence of product yield showed that cyclohexyl-t radicals which are fornaed by recoil T atom addition to cyclohexene decomposed unimolecularly to give n-hexene-t, 1-butene-t, and methane-t with rate constant 8 x 10/sup 3/, 3 x 10/sup 4/, and 5 x 10/sup 2/ s/sup -1/, respectively . The relative nate of abstraction vs addition of radicals in alkenes was determined from the scavenger dependence of the yields of products with a nadical precursor. (40 references) (auth)

Effects of inelastic processes on the collision distribution in recoil systems

The collisional distribution function for recoil hot atom systems is examined to determine the influence of specific inelastic processes on the collision density over the reactive energy range. The inelastic processes considered result from collisional dissociation of target molecules. In the case of recoil tritium reaction with deuterium gas, it was found that the collisional distribution function was lowered due to dissociative collisions. The modified collision density incorporating inelastic events was used in this system to calculate the hot yields of DT as a function of inert gas moderation for comparison with experimental data. Both the magnitude and shape of the experimental yield curve were well represented over the entire range of moderator concentrations.

Scavenger effects in the recoil tritium reactions of cyclohexene

The comparative efficiency of H 2S, butadiene- d 5, O 2 and SO 2 as radical scavengers has been determined in the T + cyclohexene gas phase system. The T was produced by recoil in the 3He( n, p)T reaction. Direct tritium substitution on cyclohexene yields cyclohexene- t which may undergo unimolecular decomposition to produce butadiene- t. In unscavenged samples butadiene- t is selectively depleted by reactions with H atoms produced by radiolysis. Neither SO 2 nor H 2S is sufficiently reactive with H atoms to protect butadiene- t from such depletion. The “hot” butadiene- t yield can only be determined by means of O 2 or butadiene- d 6 scavenging. All products except butadiene- t exhibit normal behavior with O 2, SO 2 or H 2S scavenging.