First spectroscopic evidence for a muonium-containing molecule: NeMu* chemiluminescence

Abstract

Evidence for the formation of NeMu*, an isotopic analog of the Rydberg molecule NeH*, has been obtained from the observation of chemiluminescent emission in the near-infrared region. This is the first spectroscopic detection of a muonium-containing molecule. NeMu* was formed by stopping a 4 MeV muon (p/) beam in a target vessel containing 1-6 atm of Ne and ~1 Torr Ar. The wavelength spectrum of the emission, from ~680-1000 nm, was measured using a variable-wavelength filter, with a resolution of ± 12.5 nm. Lower resolution spectra were also taken with a series of long pass filters. A complete histogram of photon events vs time was collected for each wavelength. Two strong transitions are observed, centered at 818 and 943 nm. Identification of NeMu* was made by a comparison of the experimental spectrum with a simulated spectrum based on detailed ab initio calculations, extended to higher excitation levels than had heretofore been reported. Both experimental and theoretical results are reported here. Although the mechanism by which the emitting states in NeMu* are formed remains unclear, radiolysis effects appear to playa dominant role, indicating that NeMu+ (the product of muon thermalization in Ne) undergoes charge exchange with metastable Ar* and/or is neutralized by a spur electron, both species produced during the slowing down of the high energy muon.

Effects of confinement on the Rydberg molecule NeH

“…Spectroscopic parameters for the ground and excited states of NeH for ω = 0.00 are presented in table 1, and the potential energy curves are shown in figure 1. The calculated values show good agreement with the data reported by Baer et al [46] and Bondybey et al [47], except for the C 2 + state where the r e value from Bondybey et al is 0.1 au longer than the value obtained in this work. The discrepancies in r e , ν e and D e are acceptable, although the computed ν e x e are systematically about 26-36% larger than those from [46].…”

“…The calculated values show good agreement with the data reported by Baer et al [46] and Bondybey et al [47], except for the C 2 + state where the r e value from Bondybey et al is 0.1 au longer than the value obtained in this work. The discrepancies in r e , ν e and D e are acceptable, although the computed ν e x e are systematically about 26-36% larger than those from [46]. Accordingly, the truncated MRCI method is still able to yield potential energy curves with good accuracy for the study of influence of confinement.…”

“…The H-36 basis set has been tested in atomic calculation of hydrogen atom, and it yielded superior excitation energies for 2s, 2p, 3s, 3p and 4s states [44] with the average error of only 0.2 × 10 −6 au. Baer et al have pointed out that the correlation effect between the Rydberg electron and the molecular core is very small and the excited states could be well described by a single configuration [46]. Previous calculations [16,47,48] and the present study also support the single dominant reference configuration.…”