RRKM Theory—Isomerization of Methyl Isocyanide

Critique of RRKM Theory—Isomerization of Methyl Isocyanide 

The RRKM theory was designed to account for the pressure dependence of the unimolecular rate constant. The theory has been successfully applied to many reactions, e.g., cyclopropane propene, CgHg C2H4 + and CH3NC Of these the latter is a particularly 

Making reasonable estimates of the molecular parameters and adjusting d to make theory and experiment coincide when k jk = 0.1 yields the results of Fig. 9.10. The corresponding values of d are given in Table 9.3. The agreement between theory and experiment is gratifying. An indication of the theory s consistency is the behavior of d. Its temperature variation is small and its value is very close to the hard-sphere diameter determined from viscosity measurements, 0.45 nm. 

Both observations suggest that the observed agreement is not fortuitous since d, in RRKM theory, establishes the cross section for collisions in which there is substantial energy transfer. In any reasonable theory this cross section must be close to that which determines the transport coefficients and must not be very temperature sensitive. 

The structure of the critical configuration was tested by means of isomerization studies on a series of isocyanides CD3NC, CH2DNC, C2H5NC, and C2D5NC. With the same critical configuration as was 

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