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Bimolecular Recombination Reactions: K‑Adiabatic and K‑Active Forms of RRKM Theory, Nonstatistical Aspects, Low-Pressure Rates, and Time-Dependent Survival Probabilities with Application to Ozone. 2

Ghaderi, Nima and Marcus, R. A. (2014) Bimolecular Recombination Reactions: K‑Adiabatic and K‑Active Forms of RRKM Theory, Nonstatistical Aspects, Low-Pressure Rates, and Time-Dependent Survival Probabilities with Application to Ozone. 2. Journal of Physical Chemistry A, 118 (44). pp. 10166-10178. ISSN 1089-5639. https://resolver.caltech.edu/CaltechAUTHORS:20141027-134216967

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Abstract

We consider for bimolecular recombination reactions the K-adiabatic versus the K-active forms of RRKM theory, where K is the component of the total angular momentum along the axis of least moment of inertia of the recombination product. When that product is approximately a prolate symmetric top, with two moments of inertia of the product substantially larger than the third, K becomes a dynamically slowly varying quantity and the K-adiabatic form of RRKM theory is the appropriate version to use. Using classical trajectory results for the rate constant for ozone formation in the low-pressure region as an example, excellent agreement for the recombination rate constant k_(rec) with the K-adiabatic RRKM theory is observed. Use of a two transition state (inner, outer TS) formalism also obviates any need for assessing recrossings in the exit channel. In contrast, the K-active form of RRKM theory for this system disagrees with the trajectory results by a factor of about 2.5. In this study we also consider the distribution of the (E, J) resolved time-dependent survival probabilities P(E, J, t) of the intermediate O_3^* formed from O + O_2. It is calculated using classical trajectories. The initial conditions for classical trajectories were selected using action-angle variables and a total J representation for (E, J) resolved systems, as described in Part I.1 The difference between K-active and K-adiabatic treatments is reflected also in a difference of the K-active RRKM survival probability P(E, J, t) from its trajectory-based value and from its often non-single-exponential decay. It is shown analytically that k_(rec) (K-active) ≥ k_(rec) (K-adiabatic), independent of the details of the TS (e.g., variational or fixed RRKM theory, 1-TS or 2-TS). Nonstatistical effects for O_3^* formation include a small initial recrossing of the transition state, a slow (several picoseconds) equipartitioning of energy among the two O–O bonds of the newly formed O_3^*, and a small nondissociation (a quasi-periodicity) of some trajectories originating in O_3^* (∼10%) and so, by microscopic reversibility, are not accessible from O + O_2. An apparently new feature of the present results is the comparison of classical trajectories with K-adiabatic and K-active theories for rate constants of bimolecular recombinations. The quantum mechanical counterpart of classical K-adiabatic RRKM theory is also given, and its comparison with the experimental k_(rec) for O_3 is given elsewhere.


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http://pubs.acs.org/doi/abs/10.1021/jp506788zPublisherArticle
http://dx.doi.org/10.1021/jp506788zDOIArticle
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Additional Information:© 2014 American Chemical Society. Received: July 8, 2014; Revised: September 12, 2014; Published: September 12, 2014. It is a pleasure to acknowledge the support of this research by the NSF.
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Issue or Number:44
Record Number:CaltechAUTHORS:20141027-134216967
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20141027-134216967
Official Citation:Bimolecular Recombination Reactions: K-Adiabatic and K-Active Forms of RRKM Theory, Nonstatistical Aspects, Low-Pressure Rates, and Time-Dependent Survival Probabilities with Application to Ozone. 2 Nima Ghaderi and R. A. Marcus The Journal of Physical Chemistry A 2014 118 (44), 10166-10178
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:50868
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:27 Oct 2014 21:12
Last Modified:03 Oct 2019 07:27

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