An investigation has been made of the kinetics of inclusion of rare gases in type I and type I1 clathrate structures 9 of water. It has been established that Kr and Xe can react with small ice crystals at -78"C, but not Ar. However, Ar can react very slowly with ice at -183°C. If chloro-

An investigation has been made of type I1 double hydrates, involving organic species such as chloroform with Hz, Ne, N2, Ar, 0 2 , C&, Kr, Xe, C2H4, CzH6 and C02 as "help" gases. Among these, the heavier rare gases and methane showed considerable selectivity i n their affinity for the small cavities of the host lattice. All phases were non-stoichiometric in composition : the average fraction of the larger cavities of the host lattice occupied by the main hydrate formers CHC13 and CH31 were respectively 0.95 and 096 ; these fractions for the help gases in the smaller cavities were considerably smaller, ranging from 0.0046 (H2) to 0.64 (Xe) at 700 mm pressure and about 0°C. The amounts of help gases included in the water host lattice, in the molecular sieve zeolite 13X, and dissolved in liquid water, have been compared. The fractionation through hydrate f o r m a t h of mixtures of CHC13 with CH3I, C ~H S C H ~, C6H6, CCk and CH2C12, and of the " help " gas mhtures 02+N2, Ar+K.r and Kr+Xe has been measured and compared with theoretical estimates. Theoretical aspects of the stabilizing influence of help gases have been discussed in relation to the experimental results.

The defect structure of ZrO2 and HfO2 has been studied through measurements of electrical conductivity as a function of oxygen pressure. The electrical conductivity exhibits an unusual and complex oxygen pressure dependence, and to explain the results it has been proposed that these oxides are ionic conductors and that a coupled transport of oxygen vacancies and interstitials is faster than an independent transport of these defects. Thermogravimetric measurements on ZrO2 suggest that the nonstoichiometry of this oxide is more than a factor of ten smaller than that observed by Aronson.

A study has been made of the ~nechanisms of the reactions of allyl radicals, produced thermally from diallyl, with various hydrocarbons in the temperature range 460-506' C. The allyl radical is capable of abstracting hydrogen from certain hydrocarbons and of adding to olelinic double bonds a t these temperatures. The rates of formation of the principal products in the reactions between allyl and I-butene, propylene, and ethylene are linearly related to the square root of the diallyl concentration. Mechanisms are proposed t o account for the reaction products formed. I n addition t o reacting readily with olehns the allyl radical is observed to sensitize the decomposition of n-butane a t 506' C. The implications of the present results with respect to inhibition in pyrolysis of hydrocarbons are discussed briefly. INTRODUCTIONThe information available in the literature on the reactivity of the allyl radical has been reviewed briefly in an earlier paper (1). The formation of ally1 has been proposed as the primary step in the pyrolysis of diallyl ( I ) , propylene (2), allyl bromide (3, 4), isobutene (5), and 1-butene (6). The action of propylene as an inhibitor for certain organic deco~iipositions has been commonly ascribed to the for~iiation of allyl by hydrogen abstraction from the propylene by active radicals like ~ilethyl and ethyl. I t has been fairly generally assumed that in the temperature range in which pyrolyses in static systems normally occur the ally1 radical has sufficient resonance stabilization to render it incapable of propagating reaction chains (7, p. 126). The resonance stabilization energy has been esti~iiated by Coulson (8) to be 15.4 kcal/mole and by Bolland and Gee (9) to be 18.7 kcal/mole. Semenov (10) ascribes to the allyl radical a reactivity less than that of benzyl ancl a delocalization energy of 23 Itcal/mole.The formation of ally1 has been observed directly in the pyrolysis of ally1 iodide and of cliallyl using a mass spectrometer with a flow system a t temperatures between 690 and 890" C (11). The mechanism of decomposition of this latter compound in a static system a t temperatures between 460 and 520" C can best be understoocl ( I ) on the assumption that the primarl-step involves a split into two allyl radicals which call subsequently abstract hydrogen to form propylene or add to olefinic double bonds to for111 the cyclic unsaturated products \vliicll are formed in substantial amounts. The co~iclusio~i that ally1 abstracts hydrogen readily under these conditions is in agree~iient \vith recent results of I\ilcKesby arid Gordon (12).The prcsent study mas undertalcen to demonstrate more clearly the nature of all31 reactivity and to gain further insight into the mechanism of its reaction with unsaturated hydrccarbons. Reactions with 1-butene were of particular interest because of WOI-I; done previously in this laboratory on the pyrolysis of this compound (G), the results of which provided strong evidence for reactions between it and the allyl radical. EXPERIRIIENTALThe substan...

Backscattering of 4He-ions is used to study the surfacc disorder and the surface contamination after various chemical-mechanical polishing procedures and storage conditions. The surface disorder and thc ratio between Ga and As atoms in the surface are studied after anodic oxidation on substrate samples and samples with epilayers. A deviation from stoichiometry is observed around the epilayer-substrate interface and is also caused by the anodic oxidation process itself.Nit Riickstrcuung von 4He-lonen wird die Oberflaclienfchlordnung nnd die Oberflilchenkontarnination nach vcrschiedenen chemisch--1nechanischen Polierverfahren und Aufbcwahrungsbedingungen untersucht, insbesondere dic Oberflachenfehlordnung und das Verhdtnis zwischen Ga-und As-Atornen in der Oberflachc nach anodischer Oxydation auf Substratproben und Proben niit Epitaxieschichten. Eine Abweichung von der Stochiometric wird in der Xihe der Epi-Sehicht-Substr;tt-ClrenzfIache beobachtet und wird ebenfalls durch den anodischcn OxydationsprozeD selbst vcrursacht.