Alec Wodtke

Affiliation: Max Planck Institute for Multidisciplinary Sciences

Date: Aug 11th (Fri), 2023 (17:00 – 18:00, KST) (10:00 -11:00, CET)

Title: Condensed phase tunneling from Enzyme Kinetics to Astrochemistry

Abstract: Superconducting nanowire single-photon detectors (SNSPDs) provide sufficient sensitivity to enable laser-induced fluorescence (LIF) experiments in the mid-infrared, an exciting technical development for studying molecule-surface interactions. In this talk, I will present results of experiments on the vibrational dynamics of monolayers and multilayers of solid CO adsorbed at the surface of a NaCl crystal that provide observations of quantum state resolved dynamics. When, for example, a pulsed ns laser excites CO to its v=1 state, a monochromator equipped with an SNSPD detects wavelength- and time-resolved mid-infrared emission from CO vibrational states up to v=27 that are produced by vibration-vibration (V-V) energy transfer. Kinetic Monte Carlo (kMC) simulations show that vibrational energy collects in a few CO molecules at the expense of those up to eight lattice sites away. The excited CO molecules relax by a mechanism resembling Sommerfeld’s theory of ground waves important to radio wave propagation, losing their energy to NaCl lattice-vibrations via the electromagnetic near-field. This is a weak coupling limit, where the potential energy surface is not needed to describe the relaxation process.

At high resolution, we observe new lines appearing in the infrared emission spectra, showing that CO vibrational energy converts “the right side up” where CO is bound by its C-atom to the surface to an “upside down” metastable isomer. Flipping back involves thermally activated tunneling, exhibiting a large isotope effect, where the lightest isotope is not the fastest tunneller. This is explained by a quantum rate theory of isomerization involving tunneling gateways. Near resonant states, localized on opposite sides of the isomerization barrier are coupled by collisions with a phonon bath. This represents an alternative to traditional tunneling pictures like Instanton and WKB, which are based on continuum scattering picture that is not valid in condensed phases.

*Arnab Choudhury 1,2, Jessalyn Devine 1, Dirk Schwarzer 1, Shreya Sinha 3, Peter Saalfrank 3, Alec Wodtke 1,2 1 Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany 2 Institute for physical chemistry, University of Göttingen, Göttingen, Germany 3 University of Potsdam, Potsdam Germany See Choudhury et al., Nature 612, 691–695 (2022)

To participate in the talk, please, fill out the Registration Form →