Multi-mass velocity-resolved kinetics of surface reactions at 100 kHz acquisition rate

Velocity-resolved kinetics (VRK) employs a pulsed molecular beam that initiates reactions at a surface and a pulsed ionization-laser that detects desorbed products, exploiting ion-imaging-based, velocity-sensitive detection to derive the product-flux vs reaction time. In its original form, kinetics was observed by scanning the delay between the molecular beam and laser while obtaining ion-images for ions with a single mass-to-charge ratio (m/q). Here, we demonstrate a dramatically improved version of VRK, where data are obtained quasi-continuously with a 100 kHz ionization laser and an event camera based on CERN Timepix3 technology (Amsterdam Scientific Instruments TPX3CAM). This improved version provides the full temporal behavior of the reaction products for every molecular beam pulse, resulting in a duty cycle advantage ranging from ≈ 300 to 105 in the examples given. Furthermore, the new technique allows us to simultaneously follow the kinetics of multiple species with different m/q by using the event camera's ability to provide pixel-specific timestamps. Data for three example systems, hydrogen atom recombination, hydrogen oxidation, and ammonia oxidation on Pt(332), illustrate the improvements in the acquisition rate and signal-to-noise ratio obtained. We also show that it is possible to extend the application of the VRK technique to non-stationary catalysts.