Synopsis

Detecting a Molecular Duet

Physics 10, s7
Using a scanning tunneling microscope, researchers detect coupled vibrations between two molecules.
Zhumin Han/University of California, Irvine

Molecules vibrate in many different ways—like tiny musical instruments. Nearby molecules can even vibrate in “harmony” with each other, as observed in large molecular systems. For the first time, researchers have detected such vibrational coupling between two individual molecules. The experimental technique—based on a scanning tunneling microscope (STM)—may offer a new way to study the chemical components of complex molecules.

Molecular vibrations can be studied with so-called inelastic electron tunneling spectroscopy (IETS). This technique is based on the fact that a molecule adsorbed on the tip of an STM probe (or on the surface beneath the probe) will affect the tunneling rate of electrons between probe and surface. In particular, one can identify peaks in the tunneling current spectrum as the voltage is varied. These peaks correspond to vibrational modes of the adsorbed molecule.

Wilson Ho at the University of California, Irvine, and colleagues performed IETS experiments in which carbon monoxide (CO) molecules were allowed to adsorb on both tip and surface. Working at subkelvin temperatures, the team took tunneling spectra at various tip-sample distances. The molecules repel each other at short-range distances, and this interaction can couple their vibrations. The team detected this coupling by identifying a unique peak in the tunneling spectra. They verified this identification with density-functional calculations. The observed peak shifted in frequency as the tip moved closer to the surface. Ho’s team ascribed this shift to a tilting of the CO molecules, which altered their respective alignment and the intermolecular separation. Other molecules, like OH and SH, should have unique vibrational couplings to CO, implying that one could use a CO-functionalized tip as a sensitive chemical probe.

This research is published in Physical Review Letters.

–Michael Schirber

Michael Schirber is a Corresponding Editor for Physics based in Lyon, France.


Subject Areas

Atomic and Molecular Physics

Related Articles

Designer Molecules for Fundamental-Symmetry Tests
Optics

Designer Molecules for Fundamental-Symmetry Tests

Researchers design radioactive molecules that might have exceptional sensitivity to the symmetry violations explaining the matter-antimatter imbalance of the Universe. Read More »

A Comprehensive Framework for Modeling Molecular Polaritons
Chemical Physics

A Comprehensive Framework for Modeling Molecular Polaritons

Predicting interactions between molecules and photons is now possible with a new model that combines quantum electrodynamics and a widely used formalism from quantum chemistry. Read More »

X-Ray Lasers Film Chemical Reaction in Super-Slow Motion
Chemical Physics

X-Ray Lasers Film Chemical Reaction in Super-Slow Motion

Extremely brilliant, extremely short x-ray pulses let researchers film a femtosecond-resolution movie of a chemical reaction, revealing unexpected dynamics. Read More »

More Articles