Quasi-resonant Energy-transfer In Collisions - Na2(a(1)sigma(u)(+))+k(4s)

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