RRKM unimolecular

Bunker D L and Hase W L 1973 On non-RRKM unimolecular kinetics molecules in general and CH3NC in particulars Chem. Rhys. 59 4621-32... 

By choosing the initial conditions for an ensemble of trajectories to represent a quantum mechanical state, trajectories may be used to investigate state-specific dynamics and some of the early studies actually probed the possibility of state specificity in unimolecular decay [330]. However, an initial condition studied by many classical trajectory simulations, but not realized in any experiment is that of a micro-canonical ensemble [331] which assumes each state of the energized reactant is populated statistically with an equal probability. The classical dynamics of this ensemble is of fundamental interest, because RRKM unimolecular rate theory assumes this ensemble is maintained for the reactant [6,332] as it decomposes. As a result, RRKM theory rules-out the possibility of state-specific unimolecular decomposition. The relationship between the classical dynamics of a micro-canonical ensemble and RRKM theory is the first topic considered here. 

A RRKM unimolecular system obeys the ergodic principle of statistical mechanics [337]. A quantity of more utility than N t), for analyzing the classical dynamics of a micro-canonical ensemble, is the lifetime distribution Pc t), which is defined by... 

A RRKM unimolecular system obeys the ergodic principle of statistical mechanics[JT],... 

Figure A3.12.3. Harmonic RRKM unimolecular rate constants for C2HJ—>H+C2H4 dissociation classical...

The energy loss itself is the product of the time it takes the particle to return to the barrier and the energy loss per unit time. This time, on the average is just the inverse of the RRKM unimolecular, canonical dissociation rate ... 

Table 8.5. Classical Trajectory Studies Identifying Intrinsic RRKM and non-RRKM Unimolecular Decomposition.

The calculated RRKM unimolecular rate constants for molecules containing four or five atoms increase rapidly with increasing excitation energy above decomposition threshold. As a result, the unimolecular behavior of such species is difficult to investigate except at low levels of excitation. This topic has been discussed previously in the context of recoU 8H-for-H activated CHs H (74). The ratio [Y(CH3 H)/Y(6H2 H)] increases by only about 11% over the pressure range 1-30 atm, illustrating the difficulty of obtaining complete unimolecular fallo F data for this system. 

Significance of Thermochemical Excitation Energy Distributions. Two fundamentally different approaches have been used for the elucidation of primary product excitation distributions for hot atom activated species. Many workers have utilized the RRKM unimolecular rate theory to invert pressure falloff data measured for the products from energetic H-for-H (19,64,65,74,83,84,85) or F-for-X (19,27) substitution reactions. More complete citations to the early literature are given elsewhere (57,58,59,77,80). This inversion procedure is computationally straightforward. However, it involves several a priori untested and... 

Computation of Intrinsic RRKM and Non-RRKM Unimolecular Rate Constants... 

This chapter includes a derivation of the expression of the RRKM unimolecular rate constant discussions of intrinsic RRKM and non-RRKM unimolecular dynamics, and how these dynamics are alfeeted by the classical phase space structure of energized molecules examples of intrinsic non-RRKM dynamics from experiments and simulations the role of anharmonidty in calculating accurate RRKM rate constants and quantum scattering and intrinsic RRKM and non-RRKM dynamics. 

Figure 20.4 Relationship between the nature of the vibrational spectrum versus energy and intrinsic RRKM and non-RRKM unimolecular dynamics.

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