The upper laser level of a KrF laser is treated as a cluster containing sev
eral hundreds vibration-rotation energy levels of the electronic state B, w
hich is mixed due to collisions with the close ionic state C. The KrF (C) s
tate is depleted as a result of optical transitions to a higher Rydberg sta
te. This model explains the experimental data on the picosecond dynamics of
the light amplification. The possibility of using a KrF laser as an amplif
ier of radiation with a wavelength of 120 nm is discussed.