Impingement rate and monolayer formation time τ (s)
A technique frequently used to characterize the pressure state in the high vacuum regime is the calculation of the time required to form a monomolecular or monoatomic layer on a gas-free surface, on the assumption that every molecule will stick to the surface. This monolayer formation time is closely related with the so-called impingement rate z_A. With a gas at rest the
impingement rate will indicate the number of molecules which collide with the surface inside the vacuum vessel per unit of time and surface area:
If a is the number of spaces, per unit of surface area, which can accept a specific gas, then the monolayer formation time is:
