Spectroscopic studies of neutral products of electron-ion dissociative recombination

The Flowing Afterglow Langmuir Probe (FALP) technique, in conjunction with spatially resolved absolute spectroscopy, has been applied to the dissociative recombination of CO₂+, N₂H+, HCO+, and HCO+ ions with thermal-energy electrons. The principal aim was to determine the radiative cascading contribution from high-lying triplet states, mainly CO(a′ 3Σ+) and CO(d 3Δ _i), to the total yield of the long-lived CO(a 3Π_r) state. In the case of CO₂+, the sum of the yields of the triplet states, which radiate exclusively into CO(a 3Π_r), relative to that of CO(a 3Π_r) was found to be 0.63 ± 0.08. That is, approximately 0.63 of the total CO(a ) yield is due to radiative cascade contributions from the triplet states. When combined with our previously reported value of 0.29 ± 0.101 for the total absolute yield of CO(a), the sum of absolute yields of the triplet states was found to be 0.18 ± 0.06.; A similar, but more complex analysis has been performed on HCO +/HOC+ recombination. The results indicate that CO( a) is populated mainly by direct formation from the recombination of the lower-energy isomer, HCO+. The total absolute yield of CO(a′) and CO(d) from HOC+ recombination was found to be 0.64 ± 0.20. This value represents a lower limit as not all emissions from CO( a′) could be included in the determination. The indication is that there is little direct formation of CO(a) from HOC+ recombination.; Upper and lower limits for the yield of N₂(B 3Π_g) from N₂H+ recombination were obtained, which place the absolute yield between 0.20 and 0.33. The following vibrational distributions for products of dissociative recombination were determined: CO(d 3Δ_i, ν ′ = 0–5) and CO(a′ 3Σ+, ν′ = 4–7) from CO₂+ recombination, CO(d 3Δ_i, ν′ = 0–5) and CO(a′ 3Σ +, ν′ = 5–7) from HOC+ recombination, and N₂(B 3Π _g, ν′ = 1–6) from N₂ H+ recombination.; An analysis of the O-atom yield from the dissociative recombination of H₃O+ ions employing a (2 + 1) Resonance Enhanced Multiphoton Ionization (REMPI) detection scheme was attempted. The experiments encountered problems related to poor sensitivity and excessively high background caused by contaminants within the vacuum system. Preliminary tests using a simpler (1 + 1) REMPI scheme on other species showed that only a minute fraction of the expected number ions were actually detected. No measurable signal indicating the presence of O-atoms was ever observed.