Potential energy surface hydrogen-exchange reaction

Fig. 1. Potential energy surface and classical trajectory calculations on the H + H2 hydrogen exchange reaction. Note the orbiting trajectory in the vicinity of Lake Eyring . Despite the unrealistic nature of a well near the transition state of this reaction, many of the modern ideas of chemical reaction theory can be seen in action already in this work. (See Ref. 1.)...

Studies of the Hydrogen-Exchange Reaction The Reaction of H and D Atoms with T2 Molecules. The hydrogen exchange reaction serves as a prototype for bimolecular gas-phase exchange reactions and occupies a position of fundamental importance in the development of chemical kinetics (18,33). Much attention has been lavished on this system both in the calculation of potential energy surfaces and in theo-... 

Still simple but already realistic thermally activated reaction is the hydrogen exchange reaction H + H2 H2 + H. Results below consider this reaction in full nine dimensions on the Boothroyd-Keogh-Martin-Peterson (BKMP2) reactive potential energy surface [79-81]. The transition state of this system is coUinear with equal bond lengths... 

The hydrogen exchange reaction H -I- H2 H2 + H is the simplest of all neutral reactions. It can be studied experimentally using isotopes (D + H2 —> DH + H) or ortho- and para-H2, i.e. H + para-H2 —> ortho-H2 -H H. In para-H2 the nuclear spins are anti-parallel in ortho-H2 the nuclear spins are parallel. Eyring and Polanyi (1931) carried out the first quantum-mechanical calculation of the H3 potential surface, but the remarkable fact is that it was not until 1965 that Kuntz, Nemeth and l.C. Polanyi using the London equation calculated the PES for H3. In contrast, an extensive body of data from crossed-beam reaction studies and modern and accurate ab initio calculations (see below) demonstrate that there is no potential well but a saddle point on the H3 energy surface. 

Exercise 1.9. Evaluate the potential surface for the H+H2— H2 + H exchange reaction and determine the energy of the transition state obtained with r12 = r23 = 1.4 A relative to the minimum energy of the system when one hydrogen atom is at infinity. 

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