INFRARED SPECTRA OF THE 2-CHLOROPROPYL RADICAL IN SOLID PARA-HYDROGEN
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Date
2012
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Publisher
Ohio State University
Abstract
The reaction of chlorine atoms with propylene and one of its deuterium isotopomers in solid $para$-hydrogen ($p$-H$_{2}$) matrices at 3.2 K has been studied using infrared spectroscopy. Irradiation at 365 nm of a co-deposited mixture of Cl$_{2}$, C$_{3}$H$_{6}$, and $p$-H$_{2}$ at 3.2 K produces a series of new lines in the infrared spectrum. Several of the new lines are readily assigned to the gauche and trans conformers of 1,2-dichloropropane (CH$_{3}$CHClCH$_{2}$Cl) resulting from the addition of two Cl atoms to C$_{3}$H$_{6}$. Weak lines observed at 802 and 975 cm$^{-1}$ and at 813 and 981 cm$^{-1}$ that become more prominent upon secondary irradiation at 254 and 214 nm are assigned to the allyl radical (C$_{3}$H$_{5}$) and an HCl-allyl radical complex (HCl-C$_{3}$H$_{5}$), respectively, 2044 (2003)}. Of the remaining lines, a strong line at 650 cm$^{-1}$ and weaker lines at 532, 1008, 1133, 1150, 1215 and 1382 cm$^{-1}$ are concluded to be due to a single carrier based on their behavior upon subsequent annealing to 4.5 K and irradiation at 254 and 214 nm. When the positions and intensities of these lines are compared to the MP2/aug-cc-pVDZ predicted vibrational spectra of the possible species that could result from the addition and abstraction reactions of one Cl atom with C$_{3}$H$_{6}$$^{a}$, the best agreement is found with the 2-chloropropyl radical (CH$_{3}$CHClCH$_{2}$$\cdot$). Isotopic experiments were performed with 3,3,3-C$_{3}$H$_{3}$D$_{3}$ and the corresponding infrared peaks due to the deuterium isotopomer of this radical (CD$_{3}$CHClCH$_{2}$$\cdot$) have also been observed. A final set of experiments were performed following irradiation of the Cl$_{2}$/C$_{3}$H$_{6}$/$p$-H$_{2}$ mixture at 365 nm, in which the matrix was irradiated with filtered infrared light from a globar source, which has been shown to induce a reaction between isolated Cl atoms and matrix H$_{2}$ to produce HCl and H atoms, 3124 (2006)}. In our experiments, the major products observed after infrared irradiation are HCl, 2-chloropropane (CH$_{3}$CHClCH$_{3}$) and the isopropyl radical (CH$_{3}$CH$\cdot$CH$_{3}$) and the possible mechanisms of formation of these species will be discussed.
Description
Author Institution: School of Science, Penn State Erie, Erie, PA 16563; Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu 30010, Taiwan and Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan