89.6 Rate Theories of elementary reaction 9.6.2 Calculation of ZaB SCT assumes that molecules can be taken as rigid ball without inner structure +d AB Definition: mean collision diameter: dAB9.6.2 Calculation of ZAB SCT assumes that molecules can be taken as rigid ball without inner structure. dA dB Definition: mean collision diameter: dAB AB A B d d d  =      + 2 §9.6 Rate Theories of elementary reaction