The chemiluminescent reactions Ba+N₂O and BaH-O³ in solid argon

Visible chemiluminescence in the spectral region 5500-7300 Å due to the Ba + N₂O and Ba + O₃ reactions is observed in argon matrices at temperatures below 15 K. Emission is recorded both as thermoluminescence and during deposition. Two molecular progressions of BaO, with ν₀₀ = 17 035 and 17 195 cm^-1, and ω″_e = 657 and 651 cm^-1, are found and are tentatively attributed to emission in the ā ³Σ ⁺ → X̃ ¹Σ⁺ transition for BaO* in different matrix sites, though the à ¹Σ ⁺ → X̃ ¹Σ⁺ transition could also be involved. The presumed excitation mechanism is the reactive population of one or both of the singlet states à ¹Σ⁺ and/or Ã′ ¹Π followed by rapid intersystem crossing to the ā ³Σ⁺ state. This is the first observation of a chemiluminescent atom transfer reaction in low temperature matrices. Emission due to Ba atoms in the (6s6p¹P)→(6s ^{2 1}S) transition is also observed, apparently excited by energy transfer from BaO*, most probably from the Ã′ ¹Π state.