FIRST SPECTROSCOPIC EVIDENCE FOR A MUONIUM-CONTAINING MOLECULE - NEMU-ASTERISK CHEMILUMINESCENCE

Evidence for the formation of NeMu, an isotopic analog of the Rydberg molecule NeH, has been obtained from the observation of chemilumines cent emission in the near-infrared region. This is the first spectrosc opic detection of a muonium-containing molecule. NeMu was formed by s topping a 4 MeV muon (mu(+)) beam in a target vessel containing 1-6 at m of Ne and. similar to 1 Torr Ar. The wavelength spectrum of the emis sion, from similar to 680-1000 nm, was measured, using a variable-wave length filter, with a resolution of +/-12.5 nm. Lower resolution spect ra were also taken with a series of long pass filters. A complete hist ogram of photon events vs time was collected for each wavelength. Two strong transitions are observed, centered at 818 and 943 nm. Identific ation of NeMu was made by a comparison of the experimental spectrum w ith a simulated spectrum based on detailed ad initio calculations, ext ended to higher excitation levels than had heretofore been reported. B oth experimental and theoretical results are reported here. Although t he mechanism by which the emitting states in NeMu are formed remains unclear, radiolysis effects appear to play a dominant role, indicating that NeMu(+) (the product of muon thermalization in Ne) undergoes cha rge exchange with metastable Ar and/or is neutralized by a spur elect ron, both species produced during the slowing down of the high energy muon.