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Magnetic resonance studies of atomic hydrogen confined by solid molecular hydrogen between 6.4 and 8.2 k

University of British Columbia

Magnetic hyperfine resonance in zero magnetic field has been used to study atomic hydrogen gas confined by walls coated with solid molecular hydrogen at temperatures between 6.4 and 8.2 K. The temperature range of the experiments was limited by the nature of the atom source used to produce atoms. Measurements of the frequency shift at low atom densities (nH ≃ 8 x l0⁺¹⁶ m⁻³) have yielded a binding energy for H on H₂ of 34.04 ± 0.26 K, and a surface frequency shift of -1.16 ± 0.05 MHz. These results are in excellent agreement with those obtained by Crampton et al between 3.2 and 4.5 K. The pressure shift due to the vapour pressure of the solid H₂ was found to be -1.78 ± 0.01 x 10⁻²⁴ Hz m³. The low atom density transverse relaxation rate measurements are difficult to interpret. There seems to be a relaxation mechanism on the H₂ surface that gives a contribution beyond that associated with the dispersion of frequency shifts an atoms see from normal adsorption. The data does show that the sticking coefficent of H on H₂ is greater than 0.04. Measurements at higher atom densities (nH ≤ 9 x 10⁺¹⁸ m⁻³) gave values for the surface recombination cross length which increased from 0.5 A at 6.4 K to 1.1 A at 8.2 K. The bulk spin exchange cross section was found to agree quite well with the calculations of Berlinsky and Shizgal.

Text

2010-05-26

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http://hdl.handle.net/2429/25046

Physics

University of British Columbia

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