The Kinetics and Analysis of Very Fast Chemical Reactions

Abstract

The reactions about which I propose to speak are considered fast because they take place in times measured by microseconds and milliseconds. They comprise adiabatic processes such as explosive and pyrolytic reactions which themselves are made up of intermediate reactions involving transients of very short life, and also the isothermal reactions of atoms and radicals in both gaseous and liquid media. Reactions in this category, whose half-lives vary between 10-6 and 10-2 seconds, are not the fastest known processes: they are exceeded by ionic processes in solution, by the reactions of many electronically excited species and by the relaxation of rotational energy of molecules. They comprise, however, a very large class which until recently it had not been possible to follow kinetically or to analyse ob- 1470 The reactions about which I propose to speak are considered fast because they take place in times measured by microseconds and milliseconds. They comprise adiabatic processes such as explosive and pyrolytic reactions which themselves are made up of intermediate reactions involving transients of very short life, and also the isothermal reactions of atoms and radicals in both gaseous and liquid media. Reactions in this category, whose half-lives vary between 10-6 and 10-2 seconds, are not the fastest known processes: they are exceeded by ionic processes in solution, by the reactions of many electronically excited species and by the relaxation of rotational energy of molecules. They comprise, however, a very large class which until recently it had not been possible to follow kinetically or to analyse ob-1470 jectively. Very much had indeed been achieved by the study of the overall kinetics and stoichiometry of explosive and photochemical processes, and the various patterns of chain reactions and radical reactions which have emerged constitute an impressive inductive achievement. That the new methods of kinetic spectroscopy have confirmed in no small measure the modern deductions from reaction theory is satisfactory, but I hope to show here that they have also contributed much in their own right, and have elucidated mechanisms of chain reactions, radical processes and relaxation phenomena which were hitherto obscure.The methods of flash photolysis and kinetic spectroscopy which were discovered in our laboratory at Cambridge and developed in the beginning by Porter jectively. Very much had indeed been achieved by the study of the overall kinetics and stoichiometry of explosive and photochemical processes, and the various patterns of chain reactions and radical reactions which have emerged constitute an impressive inductive achievement. That the new methods of kinetic spectroscopy have confirmed in no small measure the modern deductions from reaction theory is satisfactory, but I hope to show here that they have also contributed much in their own right, and have elucidated mechanisms of chain reactions, radical processes and relaxation phenomena which were hitherto obscure.The methods of flash photolysis and kinet...

Recent developments in theoretical chemical kinetics

“…The first group includes studies of crossed-molecular beams (1), and studies in shock-tubes ($}), in flash photolyses (3), and in gaseous flow systems (4) In the beam investigations, the angular distribution and kinetic energy distribution of the reaction products have been measured as a function of initial velocity of reactants. At present, to be sure, almost all of the beam experiments involve alkali metal atoms as one reactant because of detection problems.…”

Biochemical Analysis

“…A text on fast reactions in solution (76) and a review on rapid mixing and sampling techniques in biochemistry (81) were published; the kinetics and analysis of very fast chemical reactions were discussed (362). Two theoretical papers considered the application of chemical relaxation to biochemical systems, in isolated reactions (107) and in two-step reactions (108).…”