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dc.contributor.authorKnight, Ronald J.en
dc.date.accessioned2019-02-15T14:32:35Z
dc.date.available2019-02-15T14:32:35Z
dc.date.issued1965
dc.identifier.urihttp://hdl.handle.net/1842/34907
dc.description.abstracten
dc.description.abstractThe initial investigations of the radiation chemistry of aqueous solutions of nitric oxide by Seddon and Sutton inferred that this solute reacts rapidly and quantitatively with all the primary species formed in the radiolysis of water to form only NO⁻₂ and N₂0, such that G(NO⁻₂) = Gₑ -ₐq + Gₕ + Gₒₕ and G(N₂O) = Gₑ -ₐq- + Gₕ. These properties suggested that NO might profitably be used as a scavenging solute to determine the radical yields in neutral solution and their variations with solute concentration and pH. These investigations have been greatly facilitated by the development of a quick and reliable technique for extracting and analysing the gaseous products N₂O and N₂. The overall reaction mechanism originally proposed has been confirmed by studies of solutions at pH 7. The initial yields of the products are in complete agreement with the stoichiometry of this mechanism, and the growth of the products calculated from the initial yields and rate constant data is consistent with the experimental results up to at least 70% consumption of NO. The disappearance of hydrogen peroxide in solutions at their natural pH at high doses is shown to be due to a thermal reaction between HNO₂ and H₂O₂ and the amount of nitrogen formed is demonstrated to be entirely consistent with the fraction of Gₑ -ₐq which would be expected to react with the accumulated N₂0. By a reasonable method of extrapolation to zero solute concentration, the radical yields obtained from 1.9 x 10⁻³M NO solutions are found to be in agreement with the values normally quoted in the literature, viz. Greducing = 2.85 and Gₒₕ = 2.35. These values are supported by the data obtained for the total yield of radicals ( G(NO⁻₂) ) over the [NO] range from 10⁻⁴M to 1.2 x 10⁻²M. G(NO⁻₂) appears to be linear with respect to [NO]¹/³ and the intercept at [NO] = 0 corresponds to the sum of the "dilute solution" values given above. From consideration of this data it is argued that the variations of the radical yields with solute concentration are due only to the scavenging of radicals from the spur regions. It is also suggested that these dilute solution yields demonstrate that 0 atoms are not formed in addition to OH radicals as proposed by Allen. Unsuccessful attempts have been made to determine an H atom yield in neutral solutions by kinetic analysis of the N₂O yields obtained from NO saturated solutions containing added NO⁻₂. The results of this investigation imply that either GH = 0, or the relative rate constants for the reactions of e-ₐq and H with NO and NO⁻₂ are very similar, i.e. 7 ± 1.5. Evidence which suggests that H atoms are formed in addition to e-ₐq in systems containing only inorganic solutes has been obtained from the product yields from NO-N₂O solutions, viz. Gₕ = 0.4 ± 0.3. The radiation chemistry of NO has been investigated over the pH range from 0.45 to 12.8. In acid solutions the N₂O yield is found to increase with decreasing pH to 3.6 ± 0.1 at pH 0.45 whilst the hydrogen yield remains constant. Due to the rapid thermal reactions of H₂O₂ with HNO₂ and NO, it is not possible to obtain either material balance or a direct measurement of Gₒₕ in these solutions. Attempts have been made to determine the fate of the H₂O₂ formed and it is suggested that after a certain nitrite (HNO₂) concentration is reached, H₂O₂ reacts exclusively with HNO₂ but that a small fraction of the pernitrous acid formed as an intermediate in the reaction decomposes to OH and NO₂ which subsequently react with NO to form HNO₂. Measurements in alkaline solution are restricted to pHs no greater than 12.8 by the thermal decomposition of NO. The radical yields are found to increase with increasing pH in agreement with the observations of Dainton and Watt, i.e. G(N₂O) increases from 3.1 ± 0.1 at pH 12 to 3.4 ± 0.15 at pH 12.8, although Gₕ₂ remains constant. H₂O₂ reacts with two molecules of NO to form two molecules of NO⁻₂ in alkaline solution and the observed nitrite yields therefore correspond to Greducing + Gₒₕ + 2GH₂O₂. The observed values are found to satisfy the conditions of material balance. By assuming values of GH₂O₂, Gₒₕ has been calculated over the whole pH range investigated. As NO must react with both H and e-ₐq to form N20, these results indicate that there are genuine pH effects which cannot be explained by the conversion of e-ₐq to H and H to e-ₐq on going from neutral to acid and from neutral to alkaline solutions respectively. The scavenging mechanisms proposed by Hayon to account for these variations are discussed and it is concluded that these are inadequate. The excited water molecule hypothesis of Dainton and Watt is tentatively accepted as the best explanation of these effects. The nitrogen yields obtained from a study of NO-N₂O solutions were found to be entirely consistent with a simple competition for eaq by NO and N₂O contrary to the findings of Seddon and Sutton who proposed the formation of the intermediate N₂O⁻ to account for the unexpectedly low NO consumption observed in these solutions. The NO consumption experiments were repeated and the results obtained were found to agree with the simple competition above. It should be noted that only in this experiment do the values obtained in the present work disagree with those obtained by Seddon. In an exploratory investigation of the 1849 A° photochemistry of NO saturated water, NO is found to absorb appreciably and to decompose to products which form NO⁻₂, N₂O and N₂ such that [NO⁻₂] = 2[N₂O] + 4[N₂] . The most likely primary acts are considered to be (a) a contact charge transfer process as proposed by Grajower and Jortner and in addition (b) the dissociation of NO to N and 0 atoms in their ground states. In the former process, one of the water molecules in the solvation shell oil an NO molecule is presumed to donate an electron to the NO molecule and the NO⁻ and OH formed are then able to escape from each other. However several aspects of this photolysis have still to be resolved.en
dc.publisherThe University of Edinburghen
dc.relation.ispartofAnnexe Thesis Digitisation Project 2019 Block 22en
dc.relation.isreferencedbyen
dc.titleStudies of the influence of nitric oxide on radiation induced reactionsen
dc.typeThesis or Dissertationen
dc.type.qualificationlevelDoctoralen
dc.type.qualificationnamePhD Doctor of Philosophyen


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