Abstract: The exchange reaction between a hydrogen atom and a hydogen molecule provi- des the simplest ease where for neutral species the concerted kinetic processes of bond breaking and bond formation can be studied experimentally and theoreti- cally. The collision dynamics of the H+H_2 system have been studied by quasi-and semielassical as well as by approximate and accurate quantum methods using semi- empirical and fitted ab initio H_3 surfaces. But both approximate approaches and close-coupling technique of the electroniclly adiabatic theory yield results of the rate constant of the exchange reaction H+H_2(v=1) which are over an order of magnitude lower than the measured total rate constant. The evident disagreement between theory and experiment for this reaction, which should be the best-under-stood of all chemical processes, surely provides a continuing theoretically and experimental challenge.
A closed-coupling differential equation of the collinear A+BC→AB+C system involving electronically excited effect has been obtained by us early, with which wa have calculated the reaction probabilities of colinear reaction H+H_2 (v=0, 1)→H_2(v′=0, 1)+H on the PK semiemperical H_3 potential energy surface.
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