PENNING IONIZATION OF SMALL MOLECULES BY METASTABLE NEON

摘要

Penning ionization electron spectroscopy (PIES) in crossed, supersonic molecular beams was used to examine the reactions of Ne* (2p53s 3P2, 3P0) with two target molecules, CO2 and C2H2. Tentative peak assignments were made for each reaction, and the collision dynamics of these reactions were also examined at various collision energies in light of the two potential model of Penning ionization. The 2.6 − 3.2 eV region of the Ne* + CO2 spectrum is assigned to a ní1 progression. The region from 2.6 − 2.0 eV is more complex, but a ní1 + 2í3 progression in addition to the ní1 progression is very likely present. The region below 2.0 eV contains a broad band of signal, but no assignments have yet been made on this region. The Ne* + C2H2 spectrum has a very well resolved í2 progression around 5 eV. The A state of the Ne* + C2H2 PIES spectrum is present, but it can't be resolved with our data. The Ne* + CO2 reaction was run at collision energies of 1.73, 1.97, 2.56, and 3.13 kcal/mol. A red shift (~ −18 meV) was found for all but the 3.13 kcal/mol energy, which was blue shifted (~ 18 meV). This small shift, combined with broad peakshapes, indicates that ionization occurs over the positive and negative regions of the Ne* + CO2 potential energy surface, that is, ionization straddles the zero-crossing point. The Ne* + C2H2 reaction was run at collision energies of 1.80, 2.37, and 2.94 kcal/mol. A decreasing blue shift with increasing collision energy was found (~ 60, 50, and 45 meV, respectively). Decreasing blue shift with increasing E is not typical and could be due to changing dynamic factors as E increases. Since the shift is significantly smaller for Ne* + CO2 than for Ne* + C2H2, we propose that the interaction between Ne* and CO2 is less repulsive than that of Ne* and C2H2 in the range of geometries over which ionization occurs.