Coherent Laser Control of the Product Distribution Obtained in the Photoexcitation of HI

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Science  06 Oct 1995:
Vol. 270, Issue 5233, pp. 77-80
DOI: 10.1126/science.270.5233.77


Active control of the distribution of products of a chemical reaction was demonstrated by using a method based on the principle of quantum mechanical interference. Hydrogen iodide (HI) molecules were simultaneously excited above their ionization threshold by two competing pathways. These paths were absorption of three ultraviolet photons of frequency ω1 and one vacuum ultraviolet photon of frequency ω3 = 3ω1. The HI+ and I+ signals were modulated as the phase between the lasers was varied, with the HI+ signal lagging by 150° ± 15°. A mechanism consisting of autoionization and predissociation is proposed.