Dispersion coefficients for the nP-nP asymptote of homonuclear alkali-metal dimers

The derivation of the dispersion coefficients for various symmetries of the lower nP-nP asymptote of the homonuclear alkali-metal dimers is presented. Using the perturbation theory the dispersion coefficients C-5 are obtained in the first order and the C-6 and C-8 coefficients are obtained in the second order in terms of double sums involving atomic radial matrix elements. The sums are separated in individual contributions of each atom by using a complex integral representation. The atomic matrix elements involving Green's functions are evaluated using the Dalgarno-Lewis method. Numerical results for the C-5, C-6, and C-8 dispersion coefficients for Li, Na, K, Rb, and Cs dimers are presented. [S1050-2947(97)08112-2].