Igor Rahinov - Video Lecture

Igor Rahinov - Video Lecture

IVS-IPSTA 2020 Online Conference December 13, 2020

Nanomaterials, Thin films, and Surface Science
Morning Session

Session chair:
David Zitoun

Bar-Ilan University


Following the microscopic pathways to energy dissipation and adsorption in molecule-metal surface encounter

Igor Rahinov

Department of Natural Sciences, The Open University of Israel


Abstract


The most common mechanism of catalytic surface chemistry is that of Langmuir and Hinshelwood (LH). In the LH mechanism, reactants adsorb, thermalize with the surface and
subsequently react. At the same time, molecular vibration is known to enhance the rates of gasphase chemical reactions as the motion associated with bond stretching facilitates the reactant molecule approach to the transition state. However, for reactions occurring on via LH mechanism on metal surfaces, relevant for heterogeneous catalysis reactions, the ability of vibrational excitation to promote reactivity is hampered by rapid dissipation of the vibrational energy of the reactant into electronic excitation of the metal within several picoseconds [2]. Our recent findings challenge this paradigm: we have demonstrated that excited vibrational states can survive longer than expected – suggesting vibrational excitation might promote or modify heterogeneously catalyzed LH-chemistry on metals. In our experiments IR laser excitation was used to prepare short pulses of vibrationally excited CO(v=2) molecules that impinged and scattered from clean Au(111) surface. By quantum-state-resolved scattering studied in temporally and spatially resolved fashion we have unambiguously demonstrated that vibrationally excited molecules, prepared in the v=2 state retain significant vibrational excitation, even after residing ~ 100 ps on Au(111). Furthermore, we show that the vibrational relaxation time can serve as an internal clock to follow the microscopic pathways of adsorption and equilibration on the surface. On the basis of molecular beam experiments and theoretical modeling we reveal the intricate interplay between physisorption and chemisorption states for the prototypical CO/Au(111) system, relevant to many other heterogeneous systems.