In recent years, interactions between light (near-field) confined in picocavities-ultrasmall spaces on the order of 10-10 meters-and matter have attracted attention in the fields of nanoscience and nanotechnology, with research rapidly advancing as the foundation for atomic-scale precision measurements and quantum optical technologies.
An international research team led by Associate Professor Takashi Kumagai from the Institute for Molecular Science/SOKENDAI, Dr. Akitoshi Shiotari from the Fritz Haber Institute of the Max Planck Society (FHI) in Germany, and Dr. Mariana Rossi from the Max Planck Institute for Structure and Dynamics of Matter (MPSD) in Germany, in collaboration with Associate Professor Toshiki Sugimoto (Institute for Molecular Science/SOKENDAI), Dr. Shuyi Liu (FHI), Professor Martin Wolf (FHI), and Dr. George Trenins (MPSD), has achieved the world's first success in observing hydrogen molecules (H2) and deuterium molecules (D2) confined through physisorption in picocavities formed between silver nano-probes and silver single-crystal substrates in low-temperature, ultra-high vacuum environments at the single-molecule level using tip-enhanced Raman spectroscopy (TERS). Their results were published in Physical Review Letters.
Provided by the Institute for Molecular Science
The research group confined hydrogen molecules-the simplest molecules-in picocavities and carried out high-precision TERS measurements to spectroscopically measure their vibrational and rotational modes. As a result, they successfully elucidated the structure and dynamics of hydrogen molecules within picocavities at the single-molecule level.
In particular, by precisely controlling the gap distance between the silver nanotip and silver single-crystal substrate and gradually changing the extremely small interactions with molecules, they discovered that only the vibrational modes of hydrogen molecules changed significantly compared with deuterium molecules. Such microscopic phenomena in picocavities could not be observed using conventional spatially averaged Raman spectroscopy or other vibrational spectroscopic methods and were proven for the first time through this single-molecule-level precision spectroscopy.
To explore the origin of this novel isotope effect, detailed theoretical analysis was performed using density functional theory (DFT) and path-integral molecular dynamics (PIMD). The analysis revealed that the quantum swelling effect-where very light hydrogen nuclei show quantum fluctuation and spread spatially at low temperatures-is the main factor behind this difference between hydrogen and deuterium.
These results deepen our understanding of light-molecule interactions in extremely confined spaces and the quantum dynamics of adsorbed molecules. Atomic-scale precision molecular spectroscopy is expected to lead to applications in next-generation nanomeasurement and quantum technologies, including functional analysis of hydrogen storage materials and energy-related materials such as those for catalytic reactions, as well as the development of single-molecule quantum control.
Journal Information
Publication: Physical Review Letters
Title: Picocavity-Enhanced Raman Spectroscopy of Physisorbed H2 and D2 Molecules
DOI: 10.1103/PhysRevLett.134.206901
This article has been translated by JST with permission from The Science News Ltd. (https://sci-news.co.jp/). Unauthorized reproduction of the article and photographs is prohibited.