QUASI-RESONANT ENERGY-TRANSFER IN COLLISIONS - NA2(A(1)SIGMA(U)(+))+K(4S)

Cross sections for electron energy transfer from the initial rotationa l state J' of the two lowest vibrational levels upsilon' = 0 and upsil on' = 1 of excited dimers Na2(A) to potassium atoms as described by Na 2(A1Sigma(u)+, upsilon'J') + K(4S) --> Na2 (X1Sigma(g)+, upsilon''J'') +K(4P)+DeltaE have been examined by laser-induced fluorescence. A stro ng increase of the cross section by as much as an order of magnitude h as been observed for those dimer upsilon'J'-levels for which the dipol e transitions are close to resonance of the 4S-4P transitions in the a tom (DeltaE < 4 cm-1). The absolute cross sections for energy transfer have been calculated by the Rabitz approximation of first-order pertu rbation theory. In the case of closest energy resonance (DeltaE = 0.9 cm-1) the cross section is Q = 7.8 x 10(-13) cm2.