IV. Processes: Top-down and Bottom-up

• Discharges of gases are created through application of electric field to a gas either with
electrodes or electrodeless (microwave). The gas breaks down and leads to a discharge
• Ionization is the key reaction that sustains the discharge.
AB + e ⇒ AB + + 2e
• Note that this sustaining reaction occurs at low gas temperatures since the energy is supplied by the
energetic electrons
Example: Thermal dissociation of N 2 is very hard. But dissociation of N 2 proceeds readily in a
discharge at moderate gas temperatures since the energy for all key reactions comes from the
electrons.
• Once the discharge is sustained, a variety of other reactions proceed.
• Electron - neutral
• Ion - neutral
• Electron - ion
• Electron - electron
• Ion - ion
• Neutral - neutral