Femtosecond photoassociation spectroscopy: coherent bond formation

The method femtosecond photoassociation spectroscopy (FPAS) is introduced and we report on its application to the study of the reaction Hg+ Hg + h ν → Hg2. Our results demonstrate coherent bond formation obtained in the femtosecond time scale from free unbound reactants. The product Hg2 is formed in the D1u state and shows a high degree of rotational anisotropy induced by the polarization of the binding femtosecond pulse.