Rates and Temperature Dependence for the Reaction of Muonic Helium with Ammonia

Temperature-dependent reaction rates have been measured for the reaction of muonic helium with ammonia 4.11H + NH3 ↔ 4.11HH + NH2 where 4.11H representsthe muonicHeatom–Hewithone electron replacedbyanegative muon–whichbehaves chemicallyasaveryheavyisotopeofhydrogen,as emphasizedbythe (nonstandard)symbol. The Arrhenius activation energy was measured as 47 ± 17 kJ/mol between 400 and 600 K. The large uncertainty easily overlaps the value of 57 kJ/mol measured for the normalH + NH3 reaction [Ko et al., J. Phys. Chem. 94 (1990) 1401], and also existing calculations.The use of NH3 as the electron donor in the production of neutral muonic He is discussed in light of the title reaction, and in comparison with alternatives Xe and CH4.