Femtosecond dynamics of Cu(H_2O)_2

摘要

The ultrafast relaxation dynamics of Cu(H_2O)_2 is investigated using femtosecond photodetachment-photoionization spectroscopy.In addition,stationary points on the Cu(H_2O)_2 anion,neutral,and cation potential energy surfaces are characterized by ab initio electronic structure calculations.Electron photodetachment from Cu~-(H_2O)_2 initiates the dynamics on the ground-state potential energy surface of neutral Cu(H_2O)_2.The resulting Cu(H_2O)_2 complexes experience large-amplitude H_2O reorientation and dissociation.The time evolution of the Cu(H_2O)_2 fragmentation products is monitored by time-resolved resonant multiphoton ionization.The parent ion,Cu~+(H_2O)_2,is not detected above background levels.The rise to a maximum of the Cu~+ signal from Cu~-(H_2O)_2,and the decay of the Cu~+(H_2O) signal from Cu~-(H_2O)_2 have similar tau approx=10ps time dependences to the corresponding signals from Cu~-(H_2O),but display clear differences at very short and long times.The experimental observations can be understood in terms of the following picture.Prompt dissociation of H_2O from nascent Cu(H_2O)_2 gives rise to a vibrationally excited Cu(H_2O) complex,which dissociates to Cu+H_2O due to coupling of H_2O internal rotation to the dissociation coordinate.This prompt dissociation removes all intra-H_2O vibrational excitation from the intermediate Cu(H_2O) fragment,which quenches the long time vibrational predissociation to Cu+H_2O previously observed in analogous experiments on Cu~-(H_2O).