Noboru Fujisaki

HYDROGEN FORMATION IN THE RADIOLYSIS OF LIQUID n-BUTANE.

The effects of a radical scavenger (C2H4) and electron scavengers (N2O or SF6) on hydrogen formation in the radiolysis of liquid n‐butane at room temperature have been studied. Further, the isotopic composition of the hydrogen from n‐C4H10–n‐C4D10, n‐C4H10–n‐C4D10—0.3M N2O, and n‐C4H10–n‐C4D10—0.15M C2H4 mixtures has been measured, and the ratios of unimolecular to bimolecular hydrogen formation determined for each mixture. Combining these results, the yields of six primary processes by which hydrogen is formed have been determined separately with the results that G (thermal hydrogen atom), G (hot hydrogen atom), and G(molecular hydrogen) are, respectively, 0.7, 1.4, and 0.6 by direct excitation and ionization and 0.5, 0.6, and 1.0 by neutralization, with probable errors ± 0.2. It is noticeable that the largest contribution is from hot hydrogen atoms produced by direct excitation and ionization.

PRIMARY PROCESSES OF HYDROGEN FORMATION IN THE GAS- AND LIQUID-PHASE RADIOLYSIS OF PROPANE.

The yield of hydrogen formed in the gas‐ and liquid‐phase radiolysis of propane has been measured in the presence of a “radical scavenger” (C2H4) and an electron scavenger (N2O or SF6). Further, the isotopic compositions of the hydrogen formed in the gas‐phase radiolyses of C3H8–C3D8, C3H8–4 mole % SF6–C3D8, and C3H8–4 mole % C2H4–C3D8 mixtures and also those in the liquid‐phase radiolyses of C3H8–C3D8, C3H8–0.4M SF6–C3D8, and C3H8–0.2M C2H4–C3D8 mixtures have been measured to determine the unimolecular fraction of hydrogen for each mixture. Combining these results, the yields of six primary processes by which hydrogen is formed have been evaluated. The results are that for the gas‐phase radiolysis G (thermal hydrogen atom), G (hot hydrogen atom), and G (unimolecular hydrogen) are, respectively, 2.5, 0.9, and 1.4 by direct excitation and ionization, and that G (thermal hydrogen atom and hot hydrogen atom) and G (unimolecular hydrogen) are, respectively, 1.9 and 0.7 by neutralization. For the liquid‐phase ...

Ultraviolet absorption spectrum of the benzyl cation observed by the pulse radiolysis of benzyl chloride

The absorption spectrum of the benzyl cation has been found to have a strong band at 303 ± 2 nm and a weak broad band near 500 nm by comparing the transient spectrum for benzyl chloride saturated with oxygen with those for the solutions of 0.5 mol dm–3 ethanol in benzyl chloride saturated with oxygen.

Kinetic isotope effects for hydrogen abstractions from n‐alkanes by hydrogen atoms in the gas phase

Kinetic isotope effects kH/kDfor the reactions H•+n‐Cn H2n+2(n‐Cn D2n+2) →kH(kD)H2(HD)+Cn H2n+1•(Cn D2n+1•) have been measured using hydrogen atoms produced in the radiolysis of water vapor. The normal alkanes investigated were n‐hexane, n‐heptane, n‐octane, n‐nonane, and n‐decane. Regardless of the chain lengths of the n‐alkanes studied, the results can be expressed within the experimental error with an Arrhenius type equation kH/kD =(0.47±0.03) exp [(9.41±0.21) kJ mol−1/RT] over the temperature range of 363–463 K. The experimental results were compared with theoretical calculations using transition‐state theory and the London–Eyring–Polanyi–Sato (LEPS) potential‐energy surface. Good agreement between experimental and calculated values was obtained when allowance was made for tunneling effects.

Barrier permeabilities for a symmetric Eckart potential as studied by the kinetic isotope effects for hydrogen/deuterium abstraction from neopentane by hydrogen atoms in the gas phase

Kinetic isotope effects kH/kD have been determined in the gas phase over the temperature range 363–473 K for the abstraction reactions [graphic omitted] where RH is an alkane and R′D is the corresponding perdeuterated alkane. The alkanes studied include some n-alkanes, cycloalkanes and branched-chain alkanes. The ratio of the Arrhenius pre-exponential factors AH/AD varies from 0.32 to 0.70 and the difference in Arrhenius activation energy ED–EH ranges from 7.1 to 11.0 kJ mol,–1 depending on the strength of the C—H bond being broken. The small A factor ratios, coupled with the large activation energy differences, are taken to indicate the importance of the tunnelling effect in these reactions. A theoretical interpretation of the kinetic isotope effects (KIEs) was made for abstraction of a hydrogen atom from neopentane within the framework of transition-state theory using a London–Eyring–Polanyi–Sato (LEPS) potential-energy surface. Approximating the LEPS profile along the reaction path by a symmetric Eckart barrier, some characteristics of tunnelling phenomena are discussed in great detail, although in an elementary way. Good agreement between experiment and theory was obtained when the barrier permeabilities were taken into consideration.