Lifetimes of Excited Alkalilike Atoms Colliding by Van der Waals Forces with Inert Gas Atoms in the Groundstate

The influence of Van der Waals forces on the lifetime of coherently excited hyperfine-states |F_im_Fi〉 and |F_im_Fi〉 of alkalilike atoms i by collissions with inert gas atoms j in the groundstate |F_jm_Fi〉 has been examined. To do this the timedependent Schrödinger equation has been solved on taking into account a static magnetic field, a radiation field and a Van der Waals force. Introducing an impact parameter model for the colliding atoms with small scattering angles which form a quasimolecule |μ〉 = |F_im_FiF_jm_Fi 〉 an expression for the cross section σ_μμ has been derived which determines the halfwidth Γ _μμ of the coherently excited states. On making use of the irreducible tensor representation the calculation of the cross-section has been reduced to the calculation of multipole transitions. The result has been applied e. g. to the coherently excited 3d¹⁰4p²P_3/2-states of Cu I colliding by dipole-dipole interaction with inert gas atoms He I, and Ar I in the ground state. The values agree well with data which have been derived from zero-level-crossing experiments.