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 H-4.11 + NH3 -> (HH)-H-4.11 + NH2 where H-4.11 represents the muonic He atom - He with one electron replaced by a negative muon - which behaves chemically as a very heavy isotope of hydrogen, as emphasized by the ( 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 normal H + 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. (C) 2012 Published by Elsevier B. V. Selection and/or peer-review under responsibility of the organizing committee of the mu sr2011 conference.