The Cage Effect in Solution and Gas Phase with Application to the

The Cage Effect in Solution and Gas Phase with Application to the Determination of Rate Constants. Richard K. Lyon. J. Am. Chem. Soc. , 1964, 86 (10),...
9 downloads 8 Views 636KB Size
JOURNAL O F T H E AMERICAN CHEMICAL SOCIETY Regislered i n U.5'. Palenl Ofice.

@

C o P v i g h l , 1964, by the American Chemical Sociely

VOLUME86, NUMBER10

MAY

20, 1964

PHYSICAL AND INORGANIC CHEMISTRY [CONTRIBUTION FROM

THE ESSO

RESEARCHAND ENGINEERING CO., P R O C E S S RESEARCH DIVISION,LINDEN,N. J . ]

The Cage Effect in Solution and Gas Phase with Application to the Determination of Rate Constants BY RICHARD K. LYON RECEIVED J U N E18, 1963 T h e hitherto not generally recognized gas phase cage effect has been demonstrated. The Samuel-Magee model' permits calculation of the recombination rate constant of methyl radicals from the observed efficiencies of t h e gas phase cage effect. The rate constant thus calculated agrees well with t h a t measured by Gomer and Kistiakowsky.z The application of this theory t o investigations of the cage effect in solution gives generally satisfactory agreement. I t is concluded t h a t the model provides a general method for obtaining rate constants from measurements of the efficiency of the cage effect.

Introduction and Definitions The fact t h a t radicals can react with each other very rapidly and t h a t they are necessarily created and destroyed in pairs produces two well known effects in solution chemistry : the diffusion controlled reaction and its obverse, the cage e f f e ~ t . ~The , ~ rate of the reaction A B + AB is given by

+

d[AB]/dt = JkR[A][B]dV/b'

=

~ R [ A ] [ B ](1)

where [ A ] [ B ]is read as the product of the local concentrations of A and B averaged over the entire volume of the solution. If A and B are formed from the same molecule (for example, by the reaction ANNB + A B Nz) then [A][B] >> [AI X [Bl for newly formed radical pairs. But [AI[B]