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Issue 30, 2012
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Reaction dynamics of CN radicals with tetrahydrofuran in liquid solutions

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Abstract

Transient, broadband infra-red absorption spectroscopy with picosecond time resolution has been used to study the dynamics of reactions of CN radicals with tetrahydrofuran (THF) and d8-THF in liquid solutions ranging from neat THF to 0.5 M THF in chlorinated solvents (CDCl3 and CD2Cl2). HCN and DCN products were monitored via their v1 (C[triple bond, length as m-dash]N stretching) and v3 (C−H(D) stretching) vibrational absorption bands. Transient spectral features indicate formation of vibrationally excited HCN and DCN, and the onsets of absorption via the fundamental bands of HCN and DCN show short (5–15 ps) delays consistent with vibrational relaxation within the nascent reaction products. This interpretation is confirmed by non-equilibrium molecular dynamics simulations employing a newly derived analytic potential energy surface for the reaction in explicit THF solvent. The rate coefficient for reactive formation of HCN (as determined from measurements on both the 110 and 310 fundamental bands) decreases with increasing dilution of the THF in CDCl3 or CD2Cl2, showing pseudo-first order kinetic behaviour for THF concentrations in the range 0.5–4.5 M, and a bimolecular rate coefficient of (1.57 ± 0.12) × 1010 M−1 s−1 is derived. Simultaneous analysis of time-dependent HCN 110 and 310 band intensities following reaction of CN with THF (3.0 M) in CD2Cl2 suggests that C−H stretching mode excitation is favoured, and this deduction is supported by the computer simulations. The results extend our recent demonstration of nascent vibrational excitation of the products of bimolecular reactions in liquid solution to a different, and more strongly interacting class of organic solvents. They serve to reinforce the finding that dynamics (and thus the topology of the reactive potential energy surface) play an important role in determining the nascent product state distributions in condensed phase reactions.

Graphical abstract: Reaction dynamics of CN radicals with tetrahydrofuran in liquid solutions

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Supplementary files

Article information


Submitted
16 Jan 2012
Accepted
27 Mar 2012
First published
27 Mar 2012

Phys. Chem. Chem. Phys., 2012,14, 10424-10437
Article type
Paper

Reaction dynamics of CN radicals with tetrahydrofuran in liquid solutions

R. A. Rose, S. J. Greaves, F. Abou-Chahine, D. R. Glowacki, T. A. A. Oliver, M. N. R. Ashfold, I. P. Clark, G. M. Greetham, M. Towrie and A. J. Orr-Ewing, Phys. Chem. Chem. Phys., 2012, 14, 10424
DOI: 10.1039/C2CP40158D

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