Determining the Molecular Structure in a Laser Electric Field: Moving Toward "Molecular Cinema"

Japan High Energy Accelerator Research Institute (KEK), University of Tokyo, Ritsumeikan University, Chiba University, Kyoto University, Quantum Science and Technology Research and Development Organization (QST), Institute of Physical and Chemical Research (RIKEN), High Bright Light Science Research Center (JASRI) Of the joint research team announced on December 12, 2016, the use of femtosecond X-ray photoelectron diffraction method, the successful determination of infrared pulsed laser field in the structure of iodine molecules.

Information on the direction of the photoelectron emission tends to be averaged in the direction of the molecule with respect to the gas phase molecules that are oriented in a random direction, and the photoelectron diffraction image can not be obtained. Therefore, in this experiment, the iodine molecule (I2) in the gas phase is irradiated with YAG laser, and the direction of I2 is unified by the electric field of the laser. After that, an XFEL pulse completely overlapping with the YAG laser in time and space was irradiated to detect the X-ray photoelectron diffraction pattern of I 2p orbit released from the iodine atom (I) in I2.

In order to establish the structure (atomic pitch) of I2 in the YAG laser electric field, the research team compared the calculated results of the photoelectron diffraction with the calculated results of the photoelectron diffraction theory that takes the ionization energy and the atomic pitch of the I 2p orbitals as parameters. The difference between the experimental and theoretical results is then presented in a two-dimensional diagram. The results show that the atomic distance of I2 in the YAG laser electric field is weakened by the action of the laser electric field and is therefore elongated compared to the atomic distance of I2 in the equilibrium structure 10%, that is 0.2 ~ 0.3 angstrom (10-10m).

Although the infrared pulse YAG laser was used this time, it is expected that the ultrahigh-speed photochemical reaction can be visualized by introducing a pump short pulse laser for activating the photochemical reaction. The result is that molecular chemistry, the ultimate visualization of photochemical reactions in space and time, has taken a major step toward implementation, with the goal of using femtosecond X-ray photoelectron diffraction to identify ultra-high-speed molecules Kinetics of photochemical reactions and explore reaction control methods.

The research has been published in Scientific Reports, December 9, 2016, an online scientific journal.