MODE-SELECTIVE INFRARED EXCITATION OF LINEAR ACETYLENE

Quantum-mechanical simulations of excitation of linear acetylene (HCCH) with a few synchronized, infrared, linearly polarized, transform-limited, subpicosecond laser pulses reveal optimal pathways for the selective laser-controlled excitation of the stretching modes in the molecule. Examples presented include a double-resonance excitation of a CH-stretching local mode state, a single-pulse excitation of a predominantly symmetrical CH-stretching state, an optimal two-pulse dissociation of the molecule into C2H + H, and a two-pulse sequence which induces stimulated emission and dumps the energy from a highly excited CH-stretching state into a CC-stretching state. The resulting optimal laser pulses fall within the capabilities of current powerful, subpicosecond, tunable light sources. The spectroscopy of the model that is relevant for finding selective excitation pathways is discussed. The wave function of the molecule is represented in a harmonic normal-mode basis, a discrete variable representation, and in an eigenstate basis. A real-time Lanczos propagator and an energy-shifted, imaginary-time Lanczos propagator are employed.