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Filming the Birth of Molecules and Accompanying Solvent Rearrangement
Lee, Jae Hyuk,Wulff, Michael,Bratos, Savo,Petersen, Jakob,Guerin, Laurent,Leicknam, Jean-Claude,Cammarata, Marco,Kong, Qingyu,Kim, Jeongho,Møller, Klaus B.,Ihee, Hyotcherl American Chemical Society 2013 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.135 No.8
<P>Molecules are often born with high energy and large-amplitude vibrations. In solution, a newly formed molecule cools down by transferring energy to the surrounding solvent molecules. The progression of the molecular and solute–solvent cage structure during this fundamental process has been elusive, and spectroscopic data generally do not provide such structural information. Here, we use picosecond X-ray liquidography (solution scattering) to visualize time-dependent structural changes associated with the vibrational relaxation of I<SUB>2</SUB> molecules in two different solvents, CCl<SUB>4</SUB> and cyclohexane. The birth and vibrational relaxation of I<SUB>2</SUB> molecules and the associated rearrangement of solvent molecules are mapped out in the form of a temporally varying interatomic distance distribution. The I–I distance increases up to ∼4 Å and returns to the equilibrium distance (2.67 Å) in the ground state, and the first solvation cage expands by ∼1.5 Å along the I–I axis and then shrinks back accompanying the structural change of the I<SUB>2</SUB> molecule.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2013/jacsat.2013.135.issue-8/ja312513w/production/images/medium/ja-2012-12513w_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja312513w'>ACS Electronic Supporting Info</A></P>
Photolysis of Br<sub>2</sub>in CCl<sub>4</sub>studied by time-resolved X-ray scattering
Kong, Qingyu,Lee, Jae Hyuk,Lo Russo, Manuela,Kim, Tae Kyu,Lorenc, Maciej,Cammarata, Marco,Bratos, Savo,Buslaps, Thomas,Honkimaki, Veijo,Ihee, Hyotcherl,Wulff, Michael International Union of Crystallography 2010 Acta crystallographica. Section A, Foundations of Vol.66 No.2
<P>A time-resolved X-ray solution scattering study of bromine molecules in CCl4is presented as an example of how to track atomic motions in a simple chemical reaction. The structures of the photoproducts are tracked during the recombination process, geminate and non-geminate, from 100 ps to 10 µs after dissociation. The relaxation of hot Br2<SUP>*</SUP>molecules heats the solvent. At early times, from 0.1 to 10 ns, an adiabatic temperature rise is observed, which leads to a pressure gradient that forces the sample to expand. The expansion starts after about 10 ns with the laser beam sizes used here. When thermal artefacts are removed by suitable scaling of the transient solvent response, the excited-state solute structures can be obtained with high fidelity. The analysis shows that 30% of Br2<SUP>*</SUP>molecules recombine directly along the<I>X</I>potential, 60% are trapped in the<I>A</I>/<I>A</I>′ state with a lifetime of 5.5 ns, and 10% recombine non-geminately<I>via</I>diffusive motion in about 25 ns. The Br-Br distance distribution in the<I>A</I>/<I>A</I>′ state peaks at 3.0 Å.</P>