title: Nonequilibrium Chemical Effects in Single-Molecule SERS Revealed by Ab Initio Molecular Dynamics Simulations.
abstract: Recent developments in nanophotonics have paved the way for achieving significant advances in the realm of single-molecule chemical detection, imaging, and dynamics. In particular, surface-enhanced Raman scattering (SERS) is a powerful analytical technique that is now routinely used to identify the chemical identity of single molecules. Understanding how nanoscale physical and chemical processes affect single-molecule SERS spectra and selection rules is a challenging task and is still actively debated. Herein, we explore underappreciated chemical phenomena in ultrasensitive SERS. We observe a fluctuating excited electronic state manifold, governed by the conformational dynamics of a molecule (4,4'-dimercaptostilbene, DMS) interacting with a metallic cluster (Ag20). This affects our simulated single-molecule SERS spectra; the time trajectories of a molecule interacting with its unique local environment dictates the relative intensities of the observable Raman-active vibrational states. Ab initio molecular dynamics of a model Ag20-DMS system are used to illustrate both concepts in light of recent experimental results.
authors.affiliation: Environmental and Molecular Sciences Laboratory and ‡Physical Sciences Division, Pacific Northwest National Laboratory , P.O. Box 999, Richland, Washington 99354, United States.
authors.forename: Sean A
authors.initials: SA
authors.lastname: Fischer
authors.affiliation: Environmental and Molecular Sciences Laboratory and ‡Physical Sciences Division, Pacific Northwest National Laboratory , P.O. Box 999, Richland, Washington 99354, United States.
authors.forename: Edoardo
authors.identifier: http://orcid.org/0000-0001-5955-0734
authors.initials: E
authors.lastname: Aprà
authors.affiliation: Environmental and Molecular Sciences Laboratory and ‡Physical Sciences Division, Pacific Northwest National Laboratory , P.O. Box 999, Richland, Washington 99354, United States.
authors.forename: Niranjan
authors.initials: N
authors.lastname: Govind
authors.affiliation: Environmental and Molecular Sciences Laboratory and ‡Physical Sciences Division, Pacific Northwest National Laboratory , P.O. Box 999, Richland, Washington 99354, United States.
authors.forename: Wayne P
authors.identifier: http://orcid.org/0000-0002-3970-9282
authors.initials: WP
authors.lastname: Hess
authors.affiliation: Environmental and Molecular Sciences Laboratory and ‡Physical Sciences Division, Pacific Northwest National Laboratory , P.O. Box 999, Richland, Washington 99354, United States.
authors.forename: Patrick Z
authors.identifier: http://orcid.org/0000-0002-6032-9006
authors.initials: PZ
authors.lastname: El-Khoury