Strong-field optical control of vibrational dynamics: Vibrational Stark effect in planar acetylene

We perform quantum mechanical simulations of vibrational excitation of planar (5D) acetylene (HCCH) with linearly polarized, intense but nonionizing, infrared laser pulses, exploring one particular pathway for exciting the HCCH molecule into a CC-stretching state via the fundamental excitation in a two-pulse scheme. We optimize the pulse widths, time centers, and carrier frequencies of the two pulses to achieve the maximal projection onto the target CC-stretching state, (0,3,0,0,0) A(1), subject to penalties related to peak electric field and pulse duration. The influences of Fermi resonance, the vibrational Stark effect, and avoided crossings on the selective excitation are discussed. Different sizes of "essential-states" representation are used and checked against the underlying 299 475-point discrete variable representation (DVR) basis. We find that an essential- states basis consisting of 362 A(1) and B-2 eigenstates represents the results of a full- grid calculation for the excitation process under study. Moreover, we demonstrate that despite the complications associated with the higher dimensionality of the 5D model, we can nevertheless exert infrared laser control over the vibrational dynamics of selective excitation. (C) 1999 American Institute of Physics. [S0021-9606(98)00540-6].