Study of He*/Ne*+Ar, Kr, N₂, H₂, D₂ Chemi-Ionization Reactions by Electron Velocity-Map Imaging

Area of Science:

• Chemical physics
• Atomic and molecular collisions
• Reaction dynamics

Background:

• Chemi-ionization reactions involve electron emission and can proceed via Penning or associative ionization pathways.
• The internal energy distribution of reactants significantly influences the outcome of these reactions.
• Understanding these dynamics is crucial for fields ranging from plasma physics to astrochemistry.

Purpose of the Study:

• To investigate the chemi-ionization of various atoms and molecules using metastable Ne and He.
• To analyze the kinetic energy of emitted electrons to determine reaction channel contributions.
• To understand the role of internal energy redistribution in Penning and associative ionization.

Main Methods:

• Utilized a crossed molecular beam experiment with state-selected metastable Ne(3P2) and He(3S1) beams.
• Employed electron velocity map imaging (e-VMI) to measure electron kinetic energy distributions.
• Used a curved magnetic hexapole for state selection of metastable species and controlled collision energies at 60 meV.

Main Results:

• Measured electron kinetic energy distributions for chemi-ionization of Ar, Kr, N2, H2, and D2 by Ne(3P2), and Ar, Kr, N2 by He(3S1).
• Estimated the branching ratios between Penning and associative ionization pathways based on electron energy distributions.
• Observed that vibrational or electronic excitation in molecules enhances internal energy conversion to ion translational energy.

Conclusions:

• The internal energy state of reactants plays a critical role in determining the branching ratios of chemi-ionization reactions.
• Electron kinetic energy analysis provides insights into the energy disposal and reaction dynamics of Penning and associative ionization.
• Molecular excitation significantly impacts the energy transfer dynamics, influencing the final product states in chemi-ionization.