Calculating E/n values

Ion-molecule collisions are affected by the electric field – giving an increased “effective” temperature of the collision. The strength of this electric field is expressed relative to the number density: E/n, where E is electric field and n is the concentration of neutral particles. This ratio is known as the reduced electric field, and is given in the unit Townsend (Td).

Below we have provided a very simple calculator that makes use of the ideal gas law to calculate molecular density from pressure and temperature values. Given the density, the voltages at the PTR reactor ends, and the effective length of the reactor, an E/n value is easily determined.

If you enter new values for anything except E/n, a new value of E/n is calculated. If you enter an E/n value, an appropriate voltage for the reactor entry is calculated.

The calculations are made as soon as you move away from the value being edited, either by clicking elsewhere with the mouse, or by hitting the tab key: