Low Temperature Physics: 36, 392 (2010); https://doi.org/10.1063/1.3432246 (8 pages)
Физика Низких Температур: Том 36, Выпуск 5 (Май 2010), c. 495-503    ( к оглавлению , назад )

Infrared studies of ortho-para conversion at Cl-atom and H-atom impurity centers in cryogenic solid hydrogen

P.L. Raston*, S.C. Kettwich, and D.T. Anderson

Department of Chemistry, University of Wyoming, Laramie, WY 82071–3838, USA
E-mail: danderso@uwyo.edu

Received February 1, 2010


We report infrared spectroscopic studies of H2 ortho-para (o/p) conversion in solid hydrogen doped with Clatoms at 2 K while the Cl + H2(v = 1) → HCl + H infrared-induced chemical reaction is occurring. The Cl-atom doped hydrogen crystals are synthesized using 355 nm in situ photodissociation of Cl2 precursor molecules. For hydrogen solids with high ortho-H2 fractional concentrations (Xo = 0.55), the o/p conversion kinetics is dominated by Cl-atom catalyzed conversion with a catalyzed conversion rate constant Kcc = 1.16(11) min–1 and the process is rate-limited by ortho-H2 quantum diffusion. For hydrogen crystals with low ortho-H2 concentrations (Xo = 0.03), single-exponential decay of the ortho-H2 concentration with time is observed which is attributed to H-atom catalyzed o/p conversion by the H-atoms produced during the infrared-induced Cl + H2 reaction. The measured H-atom catalyzed o/p conversion kinetics indicates the H-atoms are mobile under these conditions in agreement with previous ESR measurements.

PACS: 66.30.Ma Diffusion in quantum solids (supersolidity);
PACS: 67.80.F– Solids of hydrogen and isotopes;
PACS: 67.80.dj Defects, impurities, and diffusion.

Ключевые слова: solid hydrogen, quantum solid, ortho-para conversion, quantum diffusion, nuclear spin conversion, quantum mechanical tunneling.