OH (A²∑⁺) and rare gas-deuteride (NeD, ArD) excimers generated in microcavity plasmas: Ultraviolet emission spectra and formation kinetics

Emission in the ultraviolet from the A +2 electronic excited states of OH, NeD, and ArD, and the formation kinetics of these excited heteronuclear diatomics, have been investigated in microcavity plasmas generated in rare gas/ H2 O or D2 gas mixtures. Excitation transfer from the a u+3 (1u, 0u-) Rydberg state of Ar2 appears to be the dominant pathway to OH (A +2) formation in Ar H2 O vapor mixtures with total pressures of 400-800 Torr and H2 O partial pressures of 100 mTorr-3 Torr. Maximum emission on the (v′, v″) = (0,0) vibrational band of the OH (A→X) transition is observed in a 25 μm, 45 nl microcavity for 600-800 Torr Ar0.5 Torr H2 O mixtures. Comparisons of experimental and simulated fluorescence spectra show the OH [A +2 (v′ =0)] state rotational temperature to be 425 K for 600 Torr Ar100 mTorr H2 O mixtures but to rise linearly with the H2 O partial pressure and exhibit a slope of 170 KTorr H2 O for 100 mTorr≤ p H2 O ≤3 Torr. Excitation of Ne or Ar D2 gas mixtures in 50×50 arrays of Si microplasma devices generates broadband spectra, peaking in the mid-ultraviolet (λ∼280-320 nm), which are attributed to the A→X transition of the ArD or NeD excimers. The optimal D2 concentration is observed to be ∼0.5% and the primary kinetic formation mechanism for the deuterides involves D atom transfer in collisions between Ar (4s P3) and D2.