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Surface Temperature Dependence of Hydrogen Ortho-Para Conversion on Amorphous Solid Water
Hirokazu Ueta1, Naoki Watanabe1, Tetsuya Hama1
1Institute of Low Temperature Science (ILTS), Hokkaido University, Sapporo 060-0819, Japan.
Abstract:
The surface temperature dependence of the ortho-to-para conversion of H_{2} on amorphous solid water is first reported. A combination of photostimulated desorption and resonance-enhanced multiphoton ionization techniques allowed us to sensitively probe the conversion on the surface of amorphous solid water at temperatures of 9.2-16 K. Within a narrow temperature window of 8 K, the conversion time steeply varied from ∼4.1×10^{3} to ∼6.4×10^{2} s. The observed temperature dependence is discussed in the context of previously suggested models and the energy dissipation process. The two-phonon process most likely dominates the conversion rate at low temperatures.
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