Nonstatistical effects

Robert Q. Topper, Visualizing Molecular Phase Space Nonstatistical Effects in Reaction Dynamics. 

R. Q. Topper, Visualizing Molecular Phase Space Nonstatistical Effects in Reaction Dynamics, Rev. Comput. Chem. 1997, 10, 101. 

The situation when the gas is isotopically scrambled, however, is very different and indeed the experimentally observed measured quantity is also very different. When the gas is isotopically scrambled, one does not measure these specific ratios of rate constants. Instead, a statistical steady-state, such as Q -F OO QOO QO + O and in the above example O + QQ OQQ OQ + Q, exists at all energies, and now the energy distribution of the vibrationally excited intermediates is that which is dictated by the steady-state equations for the above reactions, and not by that of a vibrationally hot intermediate formed solely via one channel. Under such conditions all energies of the intermediate are statistically accessible, if not from one side of the reaction intermediate then from the other. Phrased differently, the isotopic composition of the collisionally stabilized product Q3 or QO2 or will typically differ from that of the vibrationally excited species Q or QO2, since the intrinsic lifetime of the latter is isotope-dependent, as discussed in [15]. The usual RRKM-type pressure-dependent rate expression and conventional isotope effect results, modified by the nonstatistical effect discussed earlier [15]. 

The mechanism was then revised to include the additional complication of the formation of 103 and is shown in Scheme 8.15, along with their relative CCSD(T) free energies. Any nonstatistical effect would occur in the transition from 102 to 100. A direct dynamics trajectory analysis was performed starting in the neighborhood of the TS for this step using three different functionals to generate the PES. 

Space Nonstatistical Effects in Reaction Dynamics, (b) R. Larter and K. Showalter, in Reviews in Computational Chemistry, K. B. Lipkowitz and D. B. Boyd, Eds., VCH Publishers, New York, 1997, Vol. 10, pp. 177-270. Computational Studies in Nonlinear Dynamics. 

It is assumed that the reaction path involves the formation of the complex [CH30H0CH3 ], and that the reaction proceeds through three steps (1) complex formation (ion-molecule capture), (2) intramolecular isomerization, and (3) dissociation of the complex to form products. It is reasonable to consider describing the unimolecular step (isomerization of the complex) in reactions of this kind with RRKM theory. In this particular case, the trajectory results suggest that there may be non-RRKM behavior, that is, there are nonstatistical effects in the dynamics of the complex. ... 

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