Vibrational Coherence Controls Molecular Fragmentation: Ultrafast Photodynamics of the [AgCl] Scaffold.

The recently introduced pump-probe fragmentation action spectroscopy reveals a unique observation of excited state vibrational coherence (430-460 fs) in the isolated metal complex [Ag(Cl)(dcpm))] (dcpm = bis(dicyclohexylphosphino)methane) containing the [AgCl] scaffold. After photoexcitation by an XMCT transition (260 nm) in an ion trap, an unexpected correlation between specific fragment ions (loss of HCl/Cl vs loss of dcpm) and the phase of the wave packet is probed (1150 nm). Based on ab initio calculations, we assign the primary electronically excited state and ascribe the observed coherences (72-78 cm) to contain predominantly Ag-Ag stretch character. We propose specific probe absorption and vibronic coupling at the classical turning points to switch remarkably early on between the different fragmentation pathways. The overall excited state dynamics are fitted to a multiexponential decay with time constants: 0.2-0.4/3-4/19-26/104-161 ps. These findings open new perspectives for further dynamics investigations and possible applications in photocatalysis.