Abstract
The thermally averaged depolarization cross sections, σ(T), for Mu+ electron spin exchange, have been measured by the muon spin relaxation (μSR) technique in a moderator at total pressures near 1 atm over the temperature range 88–500 K. These values are related to the thermal spin-flip cross sections of interest (σ) by a simple numerical factor. At temperatures ≳120 K, σ(T) is essentially temperature independent [with σ ], though exhibiting a slight tendency to increase with temperature. At lower temperatures, σ) decreases noticeably. Comparison with the only currently available theoretical calculations of Mu(H)+ spin-flip cross sections by Aquilanti, Grossi, and Laganà [Hyperfine Interact. 8, 347 (1981)] on the potential-energy surface of Farantos et al. [Mol. Phys. 34, 947 (1977)] gives poor agreement with the data, particularly in their temperature dependence. The present results for σ) for Mu+ qualitatively exhibit the same trend with temperature as found by Desaintfuscien and Audoin [Phys. Rev. A 13, 2070 (1976)] for H-H spin exchange over a comparable temperature range, but the H-H cross sections are, surprisingly, about four times larger. Comparisons with the experimental H+ spin-exchange cross sections of Anderle et al. [Phys. Rev. A 23, 34 (1981)] and of Gordon et al. [JETP Lett. 17, 395 (1973)], indicate a significant isotope effect, with σ(Mu). While this effect can be qualitatively understood in terms of the differing numbers of partial waves involved, detailed theoretical calculations on more recent potential-energy surfaces for are called for.
- Received 25 August 1988
DOI:https://doi.org/10.1103/PhysRevA.39.3871
©1989 American Physical Society