| It was shown experimentally and theoretically that the Gouy phase of a focused laser beam can be used to control the branching between the ionization and dissociation reactions of vinyl chloride (CH2=CHCl, VCl), acetone (CH3COCH3) and dimethyl sulfide (CH3SCH3, DMS). It was also shown that the Gouy phase may yield mechanistic information by providing a direct readout of the energy difference between different reaction channels.;A molecular beam of the sample gas was simultaneously excited with 532 and 177 nm radiation, the latter produced by frequency tripling of 532 nm in a Hg oven. The relative phase of the two beams was adjusted by passing them through a cell filled with hydrogen gas. By varying the pressure of the gas, strong modulations were observed for the product ion signals produced by the photodissociation and photoionization of VCl, acetone and DMS. When the laser was focused at the center of the molecular beam, a non-zero phase lag between the ionization and dissociation processes was observed. Larger phase lags were produced as the laser was focused away from the center of the molecular beam. Quantitative agreement with theory was obtained with no adjustable parameters. |
