title: Ultrafast 2D IR spectroscopy of the excess proton in liquid water.
abstract: Despite decades of study, the structures adopted to accommodate an excess proton in water and the mechanism by which they interconvert remain elusive. We used ultrafast two-dimensional infrared (2D IR) spectroscopy to investigate protons in aqueous hydrochloric acid solutions. By exciting O-H stretching vibrations and detecting the spectral response throughout the mid-IR region, we observed the interaction between the stretching and bending vibrations characteristic of the flanking waters of the Zundel complex, [H(H2O)2](+), at 3200 and 1760 cm(-1), respectively. From time-dependent shifts of the stretch-bend cross peak, we determined a lower limit on the lifetime of this complex of 480 femtoseconds. These results suggest a key role for the Zundel complex in aqueous proton transfer.
authors.affiliation: Department of Chemistry, Institute for Biophysical Dynamics, and James Franck Institute, The University of Chicago, Chicago, IL 60637, USA.
authors.forename: Martin
authors.initials: M
authors.lastname: Thämer
authors.affiliation: Department of Chemistry, Institute for Biophysical Dynamics, and James Franck Institute, The University of Chicago, Chicago, IL 60637, USA. Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Luigi
authors.initials: L
authors.lastname: De Marco
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Krupa
authors.initials: K
authors.lastname: Ramasesha
authors.affiliation: Department of Chemistry, Institute for Biophysical Dynamics, and James Franck Institute, The University of Chicago, Chicago, IL 60637, USA. Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Aritra
authors.initials: A
authors.lastname: Mandal
authors.affiliation: Department of Chemistry, Institute for Biophysical Dynamics, and James Franck Institute, The University of Chicago, Chicago, IL 60637, USA. tokmakoff@uchicago.edu.
authors.forename: Andrei
authors.initials: A
authors.lastname: Tokmakoff