NONADIABATIC EFFECTS IN THE BROADENING AND SHIFT OF THE K 7S-4P TRANSITION BY AR

This paper reports the use of a quantum theory of spectral line broade ning and a realistic model potential to investigate non-adiabatic and inelastic excited state atomic collisions. The fully quantum mechanica l lineshifts and widths are computed for the K 7s S-2(1/2) --> 4p P-2( 3/2) transition perturbed by Ar, using non-adiabatic theory. The effec ts of the j degeneracy and inelastic collisions for the j = 3/2 --> j = 1/2 transition are included and many validity tests are performed. T wo-parameter pseudopotentials are used, for which r(0), the radius abo ut the Ar atom, and rho, the electron density (which is assumed consta nt within r(0)) are adjustable. These parameters are varied to fit the computed shifts and widths to the experimental values over a range fr om 443 to 760 K. The contributions to the width and shift from the 7s state are larger than from the 4p state because of a shallow well in t he 7s potential around 12.5 Angstrom. The contribution of the non-adia batic and inelastic terms to the width are small, although they increa se with temperature and there are no inelastic contributions to the li neshift.