Caging Dynamics

Ultrafast Photodetachment Photoionization Spectroscopy

This form of ultrafast laser spectroscopy involves pump-probe photoelectron detachment, changing the charge state of an anion from Negative to Neutral to Positive, and therefore has been referred to as NeNeuPo or Charge Reversal Spectroscopy, in addition to PDPI spectroscopy. The purpose of PhotoDetachment PhotoIonization (NeNePO) spectroscopy is to explore the ultrafast dynamics of neutral species through electron photodetachment from precursor anions.

Anions produced in the gas jet are extracted by a 1 keV high voltage pulse which accelerates the ions along the beam axis of a series of high vacuum chambers. The nascent ion packet is mass selected with a timed mass gate and Reflectron Time-of-Flight Mass Spectrometer (TOFMS), and focused to the laser interaction region with an einzel lens. The mass selected ion beam is then crossed by 100-130 femtosecond pump and probe laser pulses. As viewed in the second animation scene above, the pump laser photon detaches the electron from the selected anion and prepares the molecular wavepacket on the neutral potential energy surface (PES). Significant dynamical processes occur as the wavepacket evolves on the neutral PES due to substantial differences in the geometry of the anion and neutral species. The temporal evolution of the neutral wavepacket is typically monitored with a probe photon which ionizes the neutral species via Resonant Enhanced MultiPhoton Ionization (REMPI). The positive ion signal is recorded at a series of time delays between the pump and probe photons to gain a picture of the neutral wavepacket propagation, and thus the dynamics on the neutral PES.