Electronic quantum dance in molecules

Scientists watch moving charge density in real-time

An international research team led by DESY scientist Tim Laarmann has for the first time been able to monitor the quantum mechanically evolving electron charge distribution in glycine molecules via direct real-time measurement. The results – obtained at DESY´s brilliant free-electron laser FLASH – are published in the scientific journal Science Advances. Better knowledge of the quantum effects in the motion of electrons at the molecular level can pave the way to controlling, optimising, and engineering ionising radiation to be used for example in radiotherapy for cancer treatment.

“The amino acid glycine is an abundant basic building block of proteins and plays part in the recognition sites on cell membranes and enzymes,“ says Laarmann. “Due to its compact nature and tendencies to form hydrogen bonds it facilitates protein folding in biomolecular reactions. Stand-alone, it is utilized as an inhibiting neurotransmitter in the central nervous system.” Glycine has also been found in space and is therefore a first signature of extra-terrestrial life. The molecular reactivity in the harsh astronomical environments is an important aspect, and in particular how isolated molecules interact with ionizing radiation is a key question in astrochemistry.

Read more on DESY website

Image: In the prump-probe experiment the glycine molecule is first ionised by the high intensity X-ray pulse from DESY’s free-electron laser FLASH (left). This induces a correlated motion of the valence electrons and holes, depicted by red an d blue lobes. After a variable time delay from 0 to 175 femtoseconds the probe pulse samples the state of the glycine ion and electron motion through further ionisation and measurement of the ionisation products (right). In this example, a time delay of 10 femtoseconds is depicted, which shows two extrema of the oscillatory electron/hole motion, i.e. a half period of the electron coherence.

Credit: DESY, David Schwickert