  The aim of this work is to find analytical expressions of the radiation force
and potential densities arising from a laser pulse propagating in a dielectric
media. In the femtosecond region the force becomes strong enough to confine
neutral particles into the pulse envelope and translate them with the group
velocity in gases. Additionally, if the trapped particles are with high
density, the probability of collision with the free atoms and molecules in air
become significant. The collision energies are in the range of 12 - 24 GeV and
high enough to ionize the neutral atoms. Thus, a new type of collision
ionization can be observed, when powerful femtosecond pulses propagate in
gaseous media.
