Infrared spectra of the 2,3-dihydropyrrol-2-yl and 2,3-dihydropyrrol-3-yl radicals isolated in solid para-hydrogen

Amicangelo, Jay C.

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https://hdl.handle.net/2142/104331 Copy

Description

Title

Infrared spectra of the 2,3-dihydropyrrol-2-yl and 2,3-dihydropyrrol-3-yl radicals isolated in solid para-hydrogen

Author(s)

Amicangelo, Jay C.

Contributor(s)

Lee, Yuan-Pern

Issue Date

2019-06-21

Keyword(s)

Radicals

Abstract

The reaction of hydrogen atoms (H) with pyrrole (\chem{C_4H_5N}) in solid $para$-hydrogen ($p$-\chem{H_2}) matrices at 3.2 K has been studied using infrared spectroscopy. The production of H atoms for reaction with \chem{C_4H_5N} was essentially a three step process. First, mixtures of \chem{C_4H_5N} and \chem{Cl_2} were co-deposited in $p$-\chem{H_2} at 3.2 K for several hours, then the matrix was irradiated with ultraviolet light at 365 nm to produce Cl atoms from the \chem{Cl_2}, and finally the matrix was irradiated with infrared light to induce the reaction of the Cl atoms with $p$-\chem{H_2} to produce HCl and H atoms. Upon infrared irradiation, a series of new lines appeared in the infrared spectrum, resulting from the products of the H + \chem{C_4H_5N} reaction. To determine the grouping of lines to distinct chemical species, secondary photolysis was performed using 533-nm and 455-nm light-emitting diodes. Based on the secondary photolysis, it was determined that the majority of the new lines belong to two distinct chemical species, designated as set A (3491.0, 2754.4, 1412.7, 1260.4, 1042.8, 963.2, 922.1, 673.6 \wn) and set B (3468.3, 2784.9, 1470.6, 1449.5, 136.3, 1266.5, 1151.1, 1098.0, 960.6, 949.5, 924.0, 860.8, 574.2 \wn). The most likely reactions to occur under the low temperature conditions in solid $p$-\chem{H_2} are the addition of the H atom to the nitrogen atom or the two carbon atoms of \chem{C_4H_5N} to produce the corresponding hydrogen atom addition radicals (H-\chem{C_4H_5N}). Quantum-chemical calculations were performed at the B3PW91/6-311++G(2d,2p) level for the three possible H-\chem{C_4H_5N} radicals in order to determine the relative energetics and the predicted vibrational spectra for each radical. The addition of the H atom to carbons 2 and 3 is predicted to be exothermic by 112.1 and 76.1 kJ/mol, respectively, while the addition of the H atom to the nitrogen is predicted to be endothermic by 67.8 kJ/mol. When the lines in set A and B are compared to the scaled harmonic and anharmonic vibrational spectra for all three possible radicals, the best agreement for set A is with the radical produced by the addition to carbon 3 (2,3-dihydropyrrol-2-yl radical) and the best agreement for set B is with the radical produced by addition to carbon 2 (2,3-dihydropyrrol-3-yl radical).

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/104331

DOI

https://doi.org/10.15278/isms.2019.FD01

Copyright and License Information

Copyright 2019 Jay C. Amicangelo

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