title: Solvent-dependent structure of molecular iodine probed by picosecond X-ray solution scattering.
abstract: The effect of solute-solvent interaction on molecular structure and reaction dynamics has been a target of intense studies in solution-phase chemistry, but it is often challenging to characterize the subtle effect of solute-solvent interaction even for the simplest diatomic molecules. Since the I2 molecule has only one structural parameter and exhibits solvatochromism, it is a good model system for investigating the solvent dependence of the solute structure. By using X-rays as a probe, time-resolved X-ray liquidography (TRXL) can directly elucidate the structures of reacting molecules in solution and can thus determine the solvent-dependent structural change with atomic resolution. Here, by applying TRXL, we characterized the molecular structure of I2 in methanol and cyclohexane with sub-angstrom accuracy. Specifically, we found that the I-I bond length of I2 is longer in the polar solvent (methanol) by ∼0.2 Å than in nonpolar solvents (cyclohexane and CCl4). Density functional theory (DFT) using 22 explicit methanol molecules well reproduces the longer I-I bond of molecular iodine in methanol and reveals that the larger bond length originates from partial negative charge filled in an antibonding σ* orbital through solvent-to-solute charge transfer.
authors.affiliation: Center for Nanomaterials and Chemical Reactions, Institute for Basic Science (IBS), Daejeon 305-701, Republic of Korea. hyotcherl.ihee@kaist.ac.kr.
authors.forename: Kyung Hwan
authors.initials: KH
authors.lastname: Kim
authors.forename: Hosung
authors.initials: H
authors.lastname: Ki
authors.forename: Jae Hyuk
authors.initials: JH
authors.lastname: Lee
authors.forename: Sungjun
authors.initials: S
authors.lastname: Park
authors.forename: Qingyu
authors.initials: Q
authors.lastname: Kong
authors.forename: Jeongho
authors.initials: J
authors.lastname: Kim
authors.forename: Joonghan
authors.initials: J
authors.lastname: Kim
authors.forename: Michael
authors.initials: M
authors.lastname: Wulff
authors.forename: Hyotcherl
authors.initials: H
authors.lastname: Ihee