Sub-doppler infrared spectroscopy of jet cooled CH2I radical: CH2 stretch vibrations and “charge-sloshing” intensity dynamics

Scrape, Preston G.

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https://hdl.handle.net/2142/100700 Copy

Description

Title

Sub-doppler infrared spectroscopy of jet cooled CH2I radical: CH2 stretch vibrations and “charge-sloshing” intensity dynamics

Author(s)

Scrape, Preston G.

Contributor(s)

• Nesbitt, David
• Lesko, Daniel
• Kortyna, Andrew

Issue Date

2018-06-20

Keyword(s)

Radicals

Abstract

Iodomethyl radical (CH2I) is relevant to atmospheric chemistry, especially marine boundary layer dynamics, with recent attention arising from its use as novel precursor for Criegee intermediates (CH2OO). As a first step towards the spectroscopic investigation of a Criegee intermediate, we have pursued high resolution characterization of the CH2I radical in our slit jet discharge spectrometer. The methyl iodide radical is generated by seeding CH2I2 into a Ne/He/H2 mixture in a pulsed slit discharge, produced through either electron dissociative attachment to form iodine anions or hydrogen abstraction of iodine, with subsequent cooling in a supersonic expansion to 16 K. Infrared absorption in the CH symmetric stretch vibrational band is observed at high single-to-noise ratio (S/N = 25:1), yielding a symmetric stretch band origin at 3046.9527 ± 0.0006 cm−1 . The sub-Doppler rotational structure is fitted to a rigid-rotor Hamiltonian with spin-rotation coupling, generating principal rotational constants and the spin-orbit coupling tensor for the vibrationally excited state. Interestingly, an extensive search for the asymmetric stretch mode yielded null results, despite simple bond-dipole model predictions of three-fold larger absorption intensities for the asymmetric vs. symmetric stretch band. We conclude that the asymmetric stretch absorption intensity must be at least a factor of 25 below that of the symmetric stretch. Ab initio calculations indicate that enhancement of the symmetric vs. asymmetric stretch intensity arises from “charge sloshing” motion of electrons in the highly polar carbon-iodine bond of the correct A1 symmetry.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/100700

DOI

10.15278/isms.2018.WD11

Copyright and License Information

Copyright 2018 Preston G. Scrape

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