ION-DIP INFRARED SPECTROSCOPY OF CRIEGEE INTERMEDIATES

Zou, Meijun

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https://hdl.handle.net/2142/122398 Copy

Description

Title

ION-DIP INFRARED SPECTROSCOPY OF CRIEGEE INTERMEDIATES

Author(s)

Zou, Meijun

Contributor(s)

• Lester, Marsha
• Roy, Tarun Kumar

Issue Date

2023-06-20

Keyword(s)

Instrument/Technique Demonstration

Abstract

In the troposphere, alkene ozonolysis produces carbonyl oxide intermediates, known as Criegee intermediates, which can undergo unimolecular decay to generate hydroxyl (OH) radicals, an important atmospheric oxidant. This study focuses on the syn conformer of the methyl-substituted Criegee intermediate (syn-CH₃CHOO) that decays via 1,4 hydrogen transfer from the methyl group to the terminal oxygen, followed by O-O bond fission to yield OH radical products. IR excitation of jet-cooled syn-CH₃CHOO in the overtone CH stretch (2νCH) region facilitates this process, leading to rapid dissociation to OH + vinoxy radicals within 10 ns.ᵃ Here, we demonstrate ion-dip infrared spectroscopy of syn-CH₃CHOO by combining bIR activation in the 2ν region with VUV photoionization (10.5 eV, preferentially probing the syn conformer) and time-CH of-flight mass spectrometry detection (m/z 60). The resultant ground state depletion spectrum is recorded and compared with that previously obtained by IR action spectroscopy with detection of OH products using laser-induced fluorescence.ᶜ The ion-dip infrared spectrum reproduces the two main features at 5987 and 6081 cm−¹, but with notable changes that are being explored. In addition, the experimental results are compared with anharmonic frequency calculations at various levels of theory, which predict a single strong absorption in the 2νCH region. Further calculations of vibrational couplings are needed to interpret the experimental observations.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

Text

Language

eng

Handle URL

https://hdl.handle.net/2142/122398

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