Ultraviolet irradiation of solid parahydrogen (pH2) matrices doped with suitable H-atom precursor molecules generates H atoms in situ through a series of photoinitiated chemical reactions; these H atoms move through the pH2 matrix via a quantum diffusion process involving the tunneling-mediated reaction H + H2 ? H2 + H. The mobile H atoms may react chemically with other species that are also embedded in the pH2 matrix; an investigation of the kinetics of these H-atom chemical reactions provides us with information about reaction dynamics in the pH2 matrix environment. A recent study of the H + N2O ? HNNO reaction in solid pH2 [Mutunga, Follett, and Anderson, J. Chem. Phys. 139, 151104 (2013)] demonstrates that this reaction exhibits strongly non-Arrhenius behavior, proceeding at measurable rates only when the temperature of the system drops below 2.4 K. A molecular-level understanding of these findings requires information about how the solid pH2 matrix environment affects the long-range entrance channel of the H + N2O reaction. Here, we carry out quantum Monte Carlo simulations of a simple model system (Ar-doped solid pH2) to investigate matrix-induced changes to long-range interactions between H atoms and other impurities embedded in solid pH2 matrices. Our results suggest that the pH2 matrix creates an effective long-range repulsion between the H atom and the Ar impurity, which we explain in terms of differential solvation energies of Ar and H atoms in solid pH2.

Diffusion of hydrogen atoms through impurity-doped solid parahydrogen

248th National Meeting (2014)

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