COMPOSITIONAL CONTROL OF ROVIBRATIONAL WAVE-PACKETS IN THE E((1)SIGMA(-2 VIA QUANTUM-STATE-RESOLVED INTERMEDIATE STATE SELECTION()(G)) SHELF STATE OF LI)

Compositional control in the preparation of rovibrational wave packets is demonstrated in the E((1) Sigma(g)(+)) state of gas-phase Lip mole cules using ultrafast pump-probe laser spectroscopy combined with quan tum-state-resolved intermediate state selection. The intermediate stat e, from which subsequent ultrafast excitation occurs, is a stationary rovibrational level in the A((1) Sigma(u)(+)) Li-2, produced by cw las er excitation from the ground X((1) Sigma(g)(+)) state. The effect tha t the intermediate state has on the final composition of the wave pack et is investigated by comparing the transients resulting from ultrafas t pump-probe excitation of two different intermediate states (v(A)=14, J(A) = 18 versus v(A) = 13, J(A) = 18). In these experiments the pump wavelength is compensated so that in each case the same E-state eigen states (v(E) = 13-18, J(E) = J(A)+/-1) make up the wave packet, but wi th different amplitudes. Theory predicts, and experiments confirm, tha t the relative amplitudes of the rovibrational eigenstates are strongl y dependent upon the intermediate state and determine the spatial and temporal evolution of the wave packet. Evidence for this includes diff erences in the observed pump-probe transients and dramatically differe nt amplitudes of the beat frequencies in the Fourier analysis of the t ime-domain transients. Theoretical three-dimensional wave packet simul ations highlight how the composition of the wave packet is used to var y its spatial and temporal evolution. (C) 1997 American Institute of P hysics.