A series of twohyphen;dimensional classical kinematic computer calculations have been made on the hypothetical exothermic exchange reaction A+BCrarr;AB+C, minus;Dgr;H=48.5 kcal moleminus;1. Product energy distribution (vibration, rotation, and translation;Evib,Erot,Etrans) was obtained as a function of initial position, impact parameter, and kinetic energy (agr;i,b, andEkini). All eight different combinations of light (Lequals;1amu) and heavy (Hequals;80amu) masses were examined. Eight different potentialhyphen;energy hypersurfaces were explored. All were obtained from an empirical extension of the Londonmdash;Eyringmdash;Polanyimdash;Sato (L.E.P.S.) method. The hypersurfaces were categorized in terms of the percentage attraction,Aperp;, and percentage repulsionRperp;, read off the collinear threehyphen;dimensional surface. This categorization was shown to be helpful in arriving at a qualitative understanding of the product energy distribution to be expected from all the mass combinations reacting on these extended L.E.P.S. hypersurfaces. However, it was also shown that theAperp;,Rperp;categorization could only be of (approximate) quantitative value in predicting product energy distribution for the case that the atomic masses satisfy the inequalitymALt;mB,mC. For all other mass combinations three types of energy release must be distinguished;attractiveenergy release (A approaching BC, at normal BC separation),mixedenergy release (A still approaching BC, while BC extends), andrepulsiveenergy release (AB at normal separation retreating from C). These three types of energy release, symbolizedA,M, andRwere defined. The value of the concept was tested by obtaining A,M, andRfor each mass combination on several energy surfaces of markedly different characteristics, from part of a single collinear trajectory, and then plottingAplus;Magainst the mean vibrational excitation, lang;Evibrang;, obtained from a representative group of trajectories on the full hypersurface. For all mass combinations on all the surfaces examined it was found that (Aplus;M)sim; lang;Evibrang;.There was a tendency on surfaces with appreciable repulsive character (significant Aperp;for the reaction A+BC to give less vibration ifAequals;Lthan ifAequals;K. This lighthyphen;atom anomaly became very marked asAperp;became large. These phenomena could be understood if it was recognized that the mixed energy release had two components;late attractiveMAandearly repulsiveMR, whose proportions on a particular energy surface were characteristic of that surface and were linked to the proportions ofAperp;andRperp;for the surface. The greatest variation in lang;Evibrang; withthe nature of the hypersurfaceoccurred for the mass combinationLplus;KK, owing to the low Mthat characterized this mass combination on all surfaces. It was again found that a potentialhyphen;energy hypersurface with a large proportion of repulsive character (Rperp;Aperp;) provided the most likely qualitative explanation for the relatively low percentage vibrational excitation found experimentally in the atomic hydrogen+halogen reactions. Of all the energy surfaces the most repulsive (largeRperp;) gave product energy distributions which were most sensitive to changes inthe masses of the reagents,owing to the fact thatMwas largelyMR. Trajectories became more complex, andEvibmore sensitive tob, the more attractive and less directional the surface. The range ofb's, verbar;bminverbar; to verbar;bmaxverbar;, leading to reaction increased (for all mass combinations) on the more attractive surfaces; at the same time reaction became restricted to small intervals ofbinstead of occurring at everybwithin the range verbar;bminverbar; to verbar;bmaxverbar;. On a highly attractive (Aperp;=87) and nondirectional surface, complex trajectories, corresponding to multiple encounters of the three atoms, became important. This was accompanied by a diminution in lang;Evibrang; and an increase in lang;Erotrang; and lang;Etransrang;, which was interpreted as a transition toward a statistical distribution of energy among the products.It was pointed out that it is a general law of motion that for any given interaction potential in any number of dimensions the dynamics of a reaction involving massesmA,mB,mC, shall be identical to that for any other massesmA*,mB*,mC*, providedmA*sol;mAequals;mB*sol;mBequals;mC*sol;mC.
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