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The direct photolyses of CH2CD2 and trans-CHDCHD were carried out at room temperature in the vacuum ultraviolet region. Kr, Xe, and Hg resonance radiations were used for photolyses. Products at the Kr lines were mainly hydrogen, acetylene, ethane, and n-butane. The ratio of acetylene/hydrogen was 2.8±0.2 at 1236 A. The photolysis of CH2CD2 gives 40% H2, 40% HD, and 20% D2. The acetylene was 12% C2H2, 62% C2HD and 26% C2D2. The relative amounts of H2, HD and D2 depend upon whether a hydrogen molecule is eliminated from two (type I process) or one (type II process) carbon atom. The remaining vinylidene rapidly rearranges to acetylene. The photolysis of trans-CHDCHD gives 17% H2, 73% HD, and 10% D2. This shows that hydrogen is formed from the trans as well as from the cis position and that the isotope effect for the type I process is slightly smaller than that for the type II process. Nearly free rotation of the molecule in its excited state is suggested. The percentages of the hydrogen isotopes produced are almost independent of exciting wavelength in both isotopic ethylenes. A comparison is made with Hg(3P1)-sensitized photolysis.

0.93. These data indicate that the vanadium-rich limit of the vanadium monosulfide homogeneity range is at approximately S/V = 0.93. CONCLUSIONThere exists in the vanadium sulfide one-phase region a second-order transition from MnP structure type to NiAs structure type. This transition is consistent with the Landau conditions for a higher order transition.The transition is unique among second-order transitions that have been observed to occur with changing composition in that there is no ordering phenomenon accompanying composition change. The nonstoichiometry is primarily due to the existence of randomly distributed sulfur vacancies in the vanadium-rich phases and randomly distributed vanadium vacancies in the sulfur-rich phases. The stability of the MnP structure type in VS seems to be associated with a particular range of electron concentrations, suggesting a bandmodel interpretation of the observed phenomenon.Pure C~ and CD, have been separately but simultaneously photolyzed at 1236 A by means of a split-cell technique in order to obtain accurate relative quantum yields for the various modes of production of H2 and D2. The split-cell technique has been used to obtain quantum yields by comparison with the C02 actinometer. Molecular elimination yields for CD4 and C~ (0.58) are found to be equal, while the H-atom yield greatly exceeds the D-atom yield. It is concluded from the results that a significant fraction of the atoms produced disappears by the association reaction M+H+CHa->C~+M. The effect of scavengers and inert gas also have been investigated. The total quantum yield for Hand H2 formation is greater than unity and fragmentation of CH2 or CHa formed in the primary process is suggested:CHrH+CH.However, the lower limit for the quantum yield for D and D2 formation is 0.76 and indicates that fragmentation of CD 2 or CDa is less important than that of the corresponding protonated species.

The relative rates of abstraction by CD3 radicals of primary, secondary, and tertiary H atoms have been measured. Using a standard rate constant for abstraction of D from acetone-d6, the following rate constants are obtained:               k(mole−1cc sec−1)CD3+CD3COCD3→CD4+CD2COCD33.5×1010T12exp(−11 100/RT),(2)CD3+(CH3)3)CD→CD4+(CH3)3C0.88×1010T12exp(−9200/RT),(3)CD3+(CH3)3CD→CD3H+CH2–CD(CH3)24.38×1010T12exp(−11 100/RT),(4)CD3+(CH3)3CH→CD3H+(CH3)3C0.70×1010T12exp(−7600/RT).(10)Isotope effects obtained are, for secondary H and D in propane kH/kD=1.04exp(1400/RT),and for tertiary H and D in isobutane kH/kD=0.80 exp(1600/RT).These isotope effects are within experimental error of that given by the general expression for the deuterium isotope effect previously proposed kH/kD=exp(1500/RT),and are in excellent correspondence with the theoretical treatment of Johnston and Rapp.

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