Ab initio calculations of the transition-state geometry and vibrational frequencies of the SN2 reaction of Cl- with CH3Cl

Susan C. Tucker, Donald G. Truhlar

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Abstract

We present ab initio geometries, energies, and frequencies at the MP2/6-31G** level for three distinct stationary points on the Cr- + CH3Cl′ → ClCH3 + Cl′- gas-phase reaction path. We compare the saddle point geometries and frequencies for several basis sets, with and without correlation energy, and we compare geometries, charge distributions, and energy differences for the two most reliable method/basis set combinations. Finally, we use the MP2/6-31G** ab initio properties to evaluate the conventional transition-state theory rate constant at 300 K. Comparison with a classical calculation is used to test the validity of classical simulation techniques for this reaction. Comparison with the experimental rate constant yields a semiempirical estimate of the barrier height of 3 kcal/mol, in reasonable agreement with our best ab initio value of 4.5 kcal/mol.

Original languageEnglish (US)
Pages (from-to)8138-8142
Number of pages5
JournalJournal of physical chemistry
Volume93
Issue number25
DOIs
StatePublished - 1989

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