Fractional revivals of vibrational wave packets in the NaK A(1)Sigma(+) state

The real-time vibrational dynamics of NaK molecules excited to the electronic A(1) Sigma(+) state has been studied isotope-selectively by means of time-resolved three-photon ionization. For (NaK)-Na-23-K-39 and (NaK)-Na-23-K-41 vibrational periods of T-A((23,39)) congruent to 441 fs and T-A((23,41)) congruent to 446 fs are determined. A detailed Fourier analysis proofs a weak perturbation of the wave packet caused by spin-orbit coupling of A and b(3)II states. Pronounced fractional revivals of the fundamental oscillation occur at T-frev(1,2(23,39)) congruent to 75 ps and T-frev(1,2(23,41)) congruent to 68 ps. Spectrograms of the real-time data nicely reveal a strong fractional revival at T-frev(1,4) = 1/2T(frev)(1,2). Further fractional revivals of weaker intensity at T-frev(1,6(23,39)) approximate to 25 ps and T-frev(1,3(23,39)) approximate to 50 ps are found for the lighter isotope. (C) 1997 Elsevier Science B.V.