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Item Interaction of Oxygen with Zinc Surfaces(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (04), 1978) Bickley, Roger I.; Metcalfe, Leonard P.The interaction of oxygen with clean zinc surfaces has been investigated in the temperature range 78-493 K. Oxygen incorporation occurs extensively at 78 K, the limiting uptake being equivalent to ~ 6 monolayers of oxygen. Above 340 K a further prolonged uptake of oxygen occurs. Isothermal and temperature programmed kinetic studies of this process show that the oxidation of zinc within the temperature range 340-493 K takes place according to a pressure independent logarithmic relationship, 0t— 0\ = k0 In (1 4-/), that appears to be related to the surface regeneration which is observed in vacuo at these temperatures. The temperature dependence of k0 gives an initial energy of activation of 28 + 2 kJ mol-1 for the logarithmic process, increasing linearly with the increasing thickness by 5 kJ mol-1 monolayer-1. Illumination of the oxidised surface with ultraviolet light provides evidence which strongly suggests that electron transfer is the rate determining step at all temperatures. At the higher temperatures (340-493 K) the dark thermal reaction seems to be limited by an electron transfer involving a zinc atom at the surface.Item Decomposition of 2,2,3,3-Tetramethylbutane in the Presence of Oxygen(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (02), 1978) Atri, Gulshan M.; Baldwin, Roy R.; Evans, Geoffrey A.; Walker, Raymond W.The oxidation of 2,2,3,3-tetramethylbutane in KCl-coated vessels has been studied between 440 and 54O°C, and over the pressure range 60-500 Torr. The results are consistent with a simple mechanism comprising reactions (l)-(3) (CH3)3C— C(CH3)3 -> 2t-C4H9 t-C4H9 + O2 —> i-C4H8 + HO2 surface HO2-> tH2O+iO2. (1) (2) (3) After allowance for a small (<20 %) contribution from a chain process, accurate Arrhenius parameters Ai = 6.0x 1016 s-1, Ei = 290.4 kJ mol-1 have been obtained by combination with Tsang’s results. From the thermochemistry of reaction (1) and literature values for k-i, values of AfJ7298 (t-Bu) = 44.0 + 4.0 kJ mob* and 5298(t-Bu) = 304.2±4.0 J K-1 mol-1 are recommended. Analysis of the products shows that ~1 % of the t-butyl radicals give isobutene oxide and over the temperature range 470-542°C, Az/Au = 13.8 and £13 — E2 = 13.0 kJ mol-1 where reaction (13) is the overall process, t-C4H9 + O2 — C4H8O+OH. (13) Reaction (13) is discussed in terms of the peroxy radical isomerisation and decomposition theory and Arrhenius parameters are suggested for the (1, 4/>) H atom transfer reaction (17) in t-butylperoxy radicals (CH3)3CO2 -> (CH3)2C(OOH)CH2. (17)Item Thermal Behaviour of y-MnO2 and Some Reduced Forms in Oxygen(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (02), 1978) Lee, John A.; Newnham, Colin E.; Tye, Frank L.The products obtained by partial chemical reduction of an electrodeposited y-manganese dioxide have been studied by thermal analysis in an oxygen environment between room temperature and 725 K. Weight loss in the temperature range 430-520 K was independent of sample composition when up to 35 % of MnIV was replaced by Mn’H Substitution of >50 % MnIV led to a dependence of weight loss on degree of reduction. With the aid of X-ray diffractometry and magnetic susceptibility measurements, these results could be explained by the formation of a single phase solid solution below ~50 % reduction and a two-phase system when greater amounts of Mn’n were incorporated into the solid. Weight loss in the neighbourhood of 630 K could be resolved into two entities. The low temperature component was associated with the phase transition from y-MnO2 to /3-MnO2 accompanied by some loss of oxygen. The high temperature component was attributed to the loss of water resulting from the decomposition of Mn(OH)4.Item Infra-red Studies of Oxygen Adsorbed on Evaporated Germanium Films(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (7), 1972) Howe, R F; Liddy, J P; Metcalfe, AThe spectra of four infra-red active species between 550 and 4000 cm-1 have been observed. A band which appears after exposure of germanium to oxygen for up to 10~6 Torr min has been identified tentatively as the O; ion adsorbed over bare germanium, a second pair of bands at 690 and 780 cm-1 after exposures between 10~6 and 10-1 Torr min are identified with a surface Ge—O—Ge group. Similarity in the logarithmic growth of the bulk oxide on germanium and the development of a band at 840 cm-1 allow identification of interstitial oxygen, and a band at 750 cm-1 confirms the existence of Ge—O“ in the surface during the growth of the bulk oxide layer as postulated by Bennett and Tompkins.1Item Interaction of Oxygen with Poly crystalline Tungsten: Part 3.—Electron Stimulated Desorption(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (7), 1972) King, David A.; Madey, Theodore E.; Yates, John T.This paper is a sequel to a detailed study of the kinetics of adsorption and desorption in the interaction of O2 with polycrystalline tungsten, in which a number of oxide and O atom states were identified by thermal desorption. In electron stimulated desorption (ESD) studies two states of adsorbed oxygen were distinguished, β1 and β2; the former has a high ESD cross section and the latter a low cross section. In this paper an attempt is made to correlate the states observed in the thermal desorption study with these β1 and β2 states. The ESD properties of the β1 state are determined, and the sticking probability for readsorption onto an oxygen-saturated surface depleted of β1 by ESD is determined as a function of the incremental oxygen coverage. The steady state between electronic desorption and readsorption from the gas phase is examined, and isotopic exchange between 16O and 18O in the β2 and β1 states is observed and characterized. The appearance of the β1 state is related in a complex way to the formation of tungsten oxides which can be thermally desorbed in the temperature range 1200–1600 K.