Unimolecular Rate Constants versus Energy and Pressure as a Convolution of Unimolecular Lifetime and Collisional Deactivation Probabilities. Analyses of Intrinsic Non-RRKM Dynamics

The Journal of Physical Chemistry. a
Shreyas Malpathak, William L Hase

Abstract

Following work by Slater and Bunker, the unimolecular rate constant versus collision frequency, kuni(ω, E), is expressed as a convolution of unimolecular lifetime and collisional deactivation probabilities. This allows incorporation of nonexponential, intrinsically non-RRKM, populations of dissociating molecules versus time, N( t)/ N(0), in the expression for kuni(ω, E). Previous work using this approach is reviewed. In the work presented here, the biexponential f1 exp(- k1 t) + f2 exp(- k2 t) is used to represent N( t)/ N(0), where f1 k1 + f2 k2 equals the RRKM rate constant k( E) and f1 + f2 = 1. With these two constraints, there are two adjustable parameters in the biexponential N( t)/ N(0) to represent intrinsic non-RRKM dynamics. The rate constant k1 is larger than k( E) and k2 is smaller. This biexponential gives kuni(ω, E) rate constants that are lower than the RRKM prediction, except at the high and low pressure limits. The deviation from the RRKM prediction increases as f1 is made smaller and k1 made larger. Of considerable interest is the finding that, if the collision frequency ω for the RRKM plot of kuni(ω, E) versus ω is multiplied by an energy transfer efficiency factor βc, the RRKM kuni(ω, E) versus ω plot may be...Continue Reading

References

Aug 1, 1952·Proceedings of the National Academy of Sciences of the United States of America·H M RosenstockH Eyring
May 16, 2007·Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics·Akira ShojiguchiMikito Toda
Sep 30, 2008·The Journal of Physical Chemistry. a·J MikoschR Wester
Feb 27, 2009·The Journal of Physical Chemistry. a·Upakarasamy Lourderaj, William L Hase
May 2, 2009·The Journal of Chemical Physics·Gregory S EzraStephen Wiggins
Jan 25, 2017·Journal of the American Chemical Society·Subha PratiharWilliam L Hase

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Citations

May 4, 2020·Mass Spectrometry Reviews·Klavs Hansen
Apr 22, 2020·Annual Review of Physical Chemistry·Bhumika Jayee, William L Hase
Nov 17, 2019·The Journal of Chemical Physics·Bhumika JayeeWilliam L Hase

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