Negative muon capture ratios for nitrogen oxide molecules

Per-atom muon capture ratios are precisely determined from characteristic muonic X-ray measurements of three nitrogen oxide samples (NO, N2O, and NO2) at pressures below 100 kPa. A higher density of covalent electrons at the N atoms relative to the O atoms is required if we explain the experimental results using the proposed muon capture models. From molecular orbit calculations, we found that the electron distributions of only the highest occupied molecular orbitals (HOMO) are dominant at the N atoms, and the electrons in the HOMO significantly contribute to the muon capture phenomena in the nitrogen oxide molecules.