Real-time observation of bond formation by using Femtosecond X-ray liquidography

The research team of the Center for Nanomaterials and Chemical Reactions at the Institute for Basic Science (IBS) has successfully visualized the entire process of bond formation in solution by using femtosecond time-resolved X-ray liquidography (femtosecond TRXL) for the first time in the world.

Every researcher's longstanding dream to observe real-time bond formation in chemical reactions has come true. Since this formation takes less than one picosecond, researchers have not been able to visualize the birth of molecules. The research team has used femtosecond TRXL in order to visualize the formation of a gold trimer complex in real time without being limited by slow diffusion.

They have focused on the process of photoinduced bond formation between gold (Au) atoms dissolved in water. In the ground (S₀) state, Au atoms are weakly bound to each other in a bent geometry by van der Waals interactions. On photoexcitation, the S0 state rapidly converts into an excited (S₁) state, leading to the formation of covalent Au-Au bonds and bent-to-linear transition. Then, the S₁ state changes to a triplet (T₁) state with a time constant of 1.6 picosecond, accompanying further bond contraction by 0.1 Å. Later, the T₁ state of the trimer transforms to a tetramer on nanosecond time scale, and Au atoms return to their original bent structure.

"By using femtosecond TRXL, we will be able to observe molecular vibration and rotation in the solution phase in real time," says Hyotcherl Ihee, the group leader of the Center for Nanomaterials at IBS, as well as the professor of the Department of Chemistry at Korea Advanced Institute of Science and Technology.

Source: Institute for Basic Science (IBS), Korea