Bond Making Captured In Real Time

To enable better understanding of chemical reactions and solute-solvent interactions, an international research team has developed a new X-ray scattering method that captures snapshots of the dynamic motions of simple molecules in solution every 10 picoseconds (J. Am. Chem. Soc., DOI: 10.1021/ja312513w). Led by Michael Wulff of the European Synchrotron Radiation Facility, in Grenoble, France, and Hyotcherl Ihee of South Korea’s Institute for Basic Science and the Korea Advanced Institute of Science & Technology, the researchers used a laser pulse to partially dissociate I₂ molecules. They then used a synchrotron X-ray pulse to track how the iodine atoms dissipate their vibrational energy by colliding with solvent molecules before recombining into I₂. Adjusting the time delay between the laser and X-ray pulses allows for 10-ps time resolution. The team found that the I–I bond distance increases from 2.65 Å to a maximum of about 4 Å before the iodine atoms draw back together. The distance increases more in cyclohexane than in the heavier solvent carbon tetrachloride. The difference in dynamics between the two systems appears to stem from how much the solvent molecules resist getting pushed around by the iodine atoms, the researchers say.