Title

Combustion Reactions Followed by Photoelectron Photoion Coincidence Spectroscopy (CRF-PEPICO)

Poster Number

24

Lead Author Affiliation

Chemistry

Additional Authors

David L. Osborn

Introduction

Multiplexed mass spectrometry coupled with photoionization by tunable vacuum ultraviolet (VUV) synchrotron radiation is a powerful tool for analysis of complex chemical systems. This technique enables the detection of multiple species and allows exploring isomeric composition through photoionization spectra. However, when three or more isomers are present in one mass-to-charge ratio, it can be challenging to identify and quantify the number of isomers present and their mole fractions.

Purpose

The central goal is the fundamental understanding of the rates, products and ultimately the mechanisms of gasphase chemical reactions.

Method

A newly designed experiment, called Combustion Reactions Followed by Photoelectron Photoion Coincidence Spectroscopy (CRF-PEPICO) dramatically increases the selectivity for analyzing gas-phase mixtures. The CRFPEPICO yields time-resolved mass selected photoelectron spectra, thus providing a more detailed fingerprint than photoionization spectra. Moreover, with velocity map imaging (VMI) setup for photoelectron detection, the full spectrum is available measuring only at a few photon energies.

Results

Halogenated methanes are known to be important sources of reactive I and Br atoms, which may further react to produce IO and BrO radicals. These species have been observed to participate in destruction of ozone in lower atmosphere. In addition, CH2I2 is believed to be responsible for the formation of ultrafine particles, thus catalyze cloud formation. The CH2I radical formation and its reaction with molecular oxygen were studied with CRFPEPICO. In this system, the reaction was initiated by photolysis of CH2I2 at 355 nm producing CH2I radical and I atom. Decays of radical concentrations have been monitored in time-resolved measurements to obtain the reaction rate coefficient with the amount of O2 being in large excess over radical concentrations. In this work, we obtained 1.73 ± 0.018 x 10-12 cm3 s-1 as a rate coefficient for CH2I + O2 reaction. A new method to further increase the dynamic range of PEPICO detection was also implemented in the CRFPEPICO experiments. By placing a set of deflection plates to temporally modulate the trajectory of the ions, the arrival time and position of the ion will depend on the deflection field at the time of passing between the plates, thus help the suppression of false coincidences.

Significance

The CRF-PEPICO is a newly designed state-of-art detection technique coupled to gas-phase kinetics experiments, primarily to study combustion processes involving unstable radicals.

Location

DeRosa University Center, Stockton campus, University of the Pacific

Format

Poster Presentation

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Combustion Reactions Followed by Photoelectron Photoion Coincidence Spectroscopy (CRF-PEPICO)

DeRosa University Center, Stockton campus, University of the Pacific

Multiplexed mass spectrometry coupled with photoionization by tunable vacuum ultraviolet (VUV) synchrotron radiation is a powerful tool for analysis of complex chemical systems. This technique enables the detection of multiple species and allows exploring isomeric composition through photoionization spectra. However, when three or more isomers are present in one mass-to-charge ratio, it can be challenging to identify and quantify the number of isomers present and their mole fractions.