Radical Formation by the Photolysis of Hydrogen Iodide at 77°K. in Alkane, Alkane—Alkene, and Alkene Matrices 1

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Composition of -Type. We have discussed the literature concerning the likely composition of "reduced C02"-similar to O-type11•30-in recent publications.31•32 The basic controversy concerns whether that species is [33][34][35] or is not31•36 similar to adsorbed CO.The present data provide evidence on the structure of O-type. Thus, we have found that ^ 2 is 3 and, previously,18 that [e] ~1. A species which would satisfy these findings is >C-OH. This composition has been suggested to correspond to CH3OHadS.37-39The rate-limiting step in CH4 oxidation at low potentials would then be >C-OH + H20 -C02 + 3H+ + 3e-(7) Summary and Conclusions(1) The species on Pt in presence of CH4 (O-type) appears to lie ca. five-eighths of the way between CH4 and CO2. One electron per site is released when this species is oxidized. A composition of >C-OH fits these observations.(2) The oxidation current of this species at 0.30 V is ca. three-eighths of the oxidation current of CH4.This suggests that it lies in the path of the main CH4 -* C02 reaction.(3) The rate-limiting step of the over-all reaction at low potentials (<0.35 V) is the oxidation of this species, viz.>C-OH + H20 -> C02 + 3H+ + 3e-(4) At higher potentials (>0.40 V), the rate-limiting step is the rate of CH4 adsorption.

Section: Introductionmentioning

confidence: 99%

Absence of hydrogen atom production in radiolysis of solid hydrocarbons

Timm¹,

Willard²

1969

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“…(3) no radical production occurs as a result of light absorption by RI; (4) light absorption and consequent radical production by DI is negligible. As will be seen, the data of the present work indicate that assumptions (3) and (4) are not valid, but do not allow a quantitative evaluation of the deviations from them. They do not alter the validity of the qualitative conclusions to be drawn from Figure 5.…”

Section: Resultsmentioning

confidence: 60%

“…(2) the rates of decay are not affected by the presence of a population of radicals and I atoms remaining from a previous illumination; and (3) the rates are independent of wide variations in the HI concentration. The only mechanism which would account for removal of Htr by reaction with a random distribution of any of these species requires20 that the rate-determining step in decay is the act of detrapping, with retrapping being highly improbable relative to removal of the H by reaction with HI or with a trapped radical or atom.…”

Section: Resultsmentioning

confidence: 99%

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Growth and decay properties of trapped hydrogen and deuterium atoms produced by the photolysis of hydriodic acid, hydriodic acid-d, and hydrobromic acid in 3MP-d14 glass. Evidence for tunneling abstraction of deuterium from carbon-deuterium bonds by hydrogen

Aditya¹,

Wilkey²,

Wang³

et al. 1979

“…Introduction Recent investigations have shown that (a) hydrogen and deuterium atoms produced by photolysis of HI in perdeuterated 3-methylpentane (3MP-d14) at 20-50°K can be trapped in the matrix and observed by their esr spectra;2 (b) photolysis of HI in perprotiated 3-methylpentane (3MP-/q4) under identical conditions does not produce trapped H atoms;2 (c) radiolysis of 3MP-di4 under conditions demonstrated to trap D atoms produced by photolysis of HI does not produce trapped D atoms. 8 The present paper reports further investigations of the photolysis of HI in 3MP-di4 and 3MP-/i14 designed to answer the following questions. atom production occur by a displacement by hot H atoms or by photolysis of DI formed by disproportionation (C6Di3 + I -* C6Di2 + DI)?…”

mentioning

confidence: 98%

Properties of trapped hydrogen and deuterium atoms produced by the photolysis of hydrogen iodide in 3MP-d14 [perdeuterated 3-methylpentane] glass

Long¹,

Willard²

1970

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Photolysis of HI dissolved in perdeuterated 3-methylpentane (3MP-di4) glass at any temperature from 4 to 50°K produces trapped H atoms and trapped D atoms observable by esr, as well as C6Di3 radicals formed by abstraction of D from the 3MP-di4 by hot H. CeH13 radicals, but no trapped H atoms, are produced by photolysis of HI in 3MP-/q4 under identical conditions, indicating a major effect of isotopic substitution on the trapping capability of the matrix. The initial quantum yield of trapped H in 3MP-cZi4 (ca. 0.03) is independent of temperature over the range of at least 20-40°K but decreases with time of photolysis until a steady-state concentration is reached, while the concentrations of CeDia and D continue to grow linearly. The fractional rate of decay of trapped H atoms following short illuminations decreases rapidly with time, but the decay curves for samples with different initial concentrations are superimposable after normalization for dose. The properties of trapped H produced in 3MP-d14 in Kel-F tubes are the same as when produced in quartz tubes. Trapped H atoms may be produced by photolysis of empty quartz tubes after certain conditions of aging and y radiolysis. Trapped D (or ) atoms are not produced by the radiolysis of 3MP-d44 (or 3MP-%i4) with or without dissolved HI present, although photolysis of HI in radiolyzed 3MP-di4 produces them. The implications of the data with respect to the mechanism of H atom trapping and decay are discussed.