Oxygen Atom Diffusion By Quantum Tunneling In Solid Parahydrogen: A New Tool To Study Low Temperature Solid State Reactions

Muddasser, Ibrahim

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https://hdl.handle.net/2142/116944 Copy

Description

Title

Oxygen Atom Diffusion By Quantum Tunneling In Solid Parahydrogen: A New Tool To Study Low Temperature Solid State Reactions

Author(s)

Muddasser, Ibrahim

Contributor(s)

Anderson, David T.

Issue Date

2022-06-24

Keyword(s)

Mini-symposium: Spectroscopy meets Chemical Dynamics

Abstract

\begin{wrapfigure}{r}{0pt} \includegraphics[scale=0.37]{O-atom-diffusion.eps} \end{wrapfigure}In quantum crystals such as solid parahydrogen (pH$_{2}$), there is considerable overlap between the wavefunctions of molecules in neighboring lattice sites, such that added chemical impurities can exchange positions with nearest-neighbor pH$_{2}$ molecules and thereby quantum diffuse through the solid. Our group and others have taken advantage of the quantum diffusion of hydrogen atoms in solid pH$_{2}$ to study various low temperature hydrogenation reactions.\footnote{F. M. Mutunga et al., \textit{J. Chem. Phys. }\textbf{154} (2021) 014302.} In this talk, we report the first experimental evidence of atomic oxygen diffusion in solid pH$_{2}$. O$_2$ doped pH$_{2}$ samples are irradiated at 193 nm to produce O($^{3}$P) atoms, and repeated FTIR spectra are collected to map out the temporal behavior during and after photolysis. The experimental proof of mobile O-atoms is provided by the formation of ozone (O$_{3}$), which forms via the barrierless \chem{O + O_2 + M \rightarrow O_3 + M} reaction. After photolysis, while the system is kept in the dark, continued growth in the O$_3$ concentration with time is detected, indicating that O-atoms are mobile and reacting with O$_2$ present in the solid. The O$_3$ growth after photolysis is fit to first-order kinetics equations to extract the rate constant. Kinetics measurements show that the O-atom reaction rate more than doubles in annealed crystals compared to as-deposited crystals. This finding is consistent with the expectation that quantum diffusion is more facile in homogeneous samples with minimum defects. In fact, some proportion of the photo-produced O-atoms get trapped in as-deposited samples and can only be made mobile by annealing the sample. Currently, we are studying the effects of the photolysis conditions, temperature, and doped O$_2$ concentration on the reaction rate constant. This study shows that O-atoms can be isolated in solid pH$_{2}$ and that they are delocalized. Through double doping experiments, we hope to develop this method to study O-atom reactions with other species under controlled low temperature conditions.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Handle URL

https://hdl.handle.net/2142/116944

DOI

https://doi.org/10.15278/isms.2022.FA09

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Copyright 2022 held by the authors

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