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Title:INFRARED SPECTRA OF THE 1-CHLOROMETHYL-1-METHYLALLYL AND 1-CHLOROMETHYL-2-METHYLALLYL RADICALS ISOLATED IN SOLID PARA-HYDROGEN
Author(s):Amicangelo, Jay C.
Contributor(s):Lee, Yuan-Pern
Subject(s):Radicals
Abstract:The reaction of chlorine atoms (Cl) with isoprene (chem{C_5H_8}) in solid $para$-hydrogen ($p$-chem{H_2}) matrices at 3.2 K has been studied using infrared spectroscopy. Mixtures of chem{C_5H_8} and chem{Cl_2} were co-deposited in $p$-chem{H_2} at 3.2 K, followed by irradiation at 365 nm to cause the photodissociation of chem{Cl_2} and the subsequent reaction of Cl atoms with chem{C_5H_8}. Upon 365 nm photolysis, a series of new lines appeared in the infrared spectrum, with the strongest appearing at 807.8 and 796.7 wn. To determine the grouping of lines to distinct chemical species, secondary photolysis was performed using a low-pressure Hg lamp in combination with various filters. Based on the secondary photolysis behavior, it was determined that the majority of the new lines belong to two distinct chemical species, designated as set A (3047.2, 1482.2, 1459.5, 1396.6, 1349.6, 1268.2, 1237.9, 1170.3, 1108.8, 807.8, 754.1, 605.6, 526.9, 472.7 wn) and set B (3112.7, 1487.6, 1382.6, 1257.7, 1229.1, 1034.8, 975.8, 942.4, 796.7, 667.9, 569.7 wn). The most likely reactions to occur between Cl and chem{C_5H_8} under the low temperature conditions in solid $p$-chem{H_2} are the addition of the Cl atom to the four distinct alkene carbon atoms to produce the corresponding chlorine atom addition radicals (chem{ClC_5H_8}). Quantum-chemical calculations were performed at the B3PW91/6-311++G(2d,2p) level of theory for the four possible chem{ClC_5H_8} radicals in order to determine the relative energetics and the predicted harmonic vibrational spectra for each radical. The calculations predict that the addition of Cl to each of the four carbons is exothermic, with relative energies of 0.0, 74.5, 67.4, and 7.9 kJ/mol for the addition to carbons 1 – 4, respectively. When the lines of set A and B are compared to the scaled harmonic vibrational spectra for all four of the possible Cl addition radicals, it is found that the best agreement for set A is with the radical produced by the addition to carbon 4 (1-chloromethyl-2-methylallyl radical) and the best agreement for set B is with the radical produced by addition to carbon 1 (1-chloromethyl-1-methylallyl radical). Therefore, the lines of set A and B are assigned to these radicals, respectively.
Issue Date:6/22/2017
Publisher:International Symposium on Molecular Spectroscopy
Citation Info:APS
Genre:CONFERENCE PAPER/PRESENTATION
Type:Text
Language:English
URI:http://hdl.handle.net/2142/97158
DOI:10.15278/isms.2017.RJ04
Date Available in IDEALS:2017-07-27


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