COLLISION CROSS-SECTIONS FOR EXCITATION-ENERGY TRANSFER IN NA-ASTERISK(3P(1 E-LEFT-RIGHT-ARROW-NA-ASTERISK(3P(3/2))+K(4S(1/2)) PROCESSES/

The cross sections for the excitation energy transfer between the 3(2) P(J) states of sodium atoms by collisions with ground-state potassium atoms have been measured by resonant Doppler-free two-photon spectrosc opy, where the population densities of directly pumped and collisional ly excited Na(3P(J))(J = 1/2, 3/2) levels were probed by counter-propa gating Na(3P(J)) --> Na(4D(3/2,) (5/2)) excitation and detected with t he thermionic diode. Cross sections of sigma(3P(1/2) --> 3P(3/2)) = 19 0 Angstrom(2) +/- 20% and sigma(3P(3/2) --> 3P(1/2)) = 100 Angstrom(2) +/- 20% were found. The theoretical calculations taking into account the long-range interaction terms R(-6), R(-8) and R(-10) yield a value sigma(3P(1/2) --> 3P(3/2)) = 165 Angstrom(2). On the basis of these l ong-range interaction potentials the differential cross section has be en calculated and compared with recently published experimental data. Very good agreement between the theoretical and experimental data was found.