Electronic structure of liquid water from polarization-dependent two-photon absorption spectroscopy

This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/130/8/10.1063/1.3078336.Two-photon absorption (2PA) spectroscopy in the range from 7 to 10 eV provides new insight on the electronic structure of liquid water. Continuous 2PA spectra are obtained via the pump-probe technique, using broadband probe pulses to record the absorption at many wavelengths simultaneously. A preresonance enhancement of the absolute 2PA cross section is observed when the pump-photon energy increases from 4.6 to 6.2 eV. The absorption cross section also depends on the relative polarization of the pump and probe photons. The variation of the polarization ratio across the spectrum reveals a detailed picture of the 2PA and indicates that at least four different transitions play a role below 10 eV. Theoretical polarization ratios for the isolated molecule illustrate the value of the experimental polarization measurement in deciphering the 2PA spectrum and provide the framework for a simple simulation of the liquid spectrum. A more comprehensive model goes beyond the isolated molecule picture and connects the 2PA spectrum with previous one-photon absorption, photoelectron, and x-ray absorptionspectroscopy measurements of liquid water. Previously unresolved, overlapping transitions are assigned for the first time. Finally, the electronic character of the vertical excited states is related to the energy-dependent ionization mechanism of liquid water

Chasing charge localization and chemical reactivity following photoionization in liquid water

This is the published version, also available here: http://dx.doi.org/10.1063/1.3664746.The ultrafast dynamics of the cationic hole formed in bulk liquid water following ionization is investigated by ab initio molecular dynamics simulations and an experimentally accessible signature is suggested that might be tracked by femtosecond pump-probe spectroscopy. This is one of the fastest fundamental processes occurring in radiation-induced chemistry in aqueous systems and biological tissue. However, unlike the excess electron formed in the same process, the nature and time evolution of the cationic hole has been hitherto little studied. Simulations show that an initially partially delocalized cationic hole localizes within ∼30 fs after which proton transfer to a neighboring water molecule proceeds practically immediately, leading to the formation of the OH radical and the hydronium cation in a reaction which can be formally written as H2O+ + H2O → OH + H3O+. The exact amount of initial spin delocalization is, however, somewhat method dependent, being realistically described by approximate density functional theory methods corrected for the self-interaction error. Localization, and then the evolving separation of spin and charge, changes the electronic structure of the radical center. This is manifested in the spectrum of electronic excitations which is calculated for the ensemble of ab initio molecular dynamics trajectories using a quantum mechanics/molecular mechanics (QM/MM) formalism applying the equation of motion coupled-clusters method to the radical core. A clear spectroscopic signature is predicted by the theoretical model: as the hole transforms into a hydroxyl radical, a transient electronic absorption in the visible shifts to the blue, growing toward the near ultraviolet. Experimental evidence for this primary radiation-induced process is sought using femtosecond photoionization of liquid water excited with two photons at 11 eV. Transient absorption measurements carried out with ∼40 fs time resolution and broadband spectral probing across the near-UV and visible are presented and direct comparisons with the theoretical simulations are made. Within the sensitivity and time resolution of the current measurement, a matching spectral signature is not detected. This result is used to place an upper limit on the absorption strength and/or lifetime of the localized H2O+ (aq) species

Chasing charge localization and chemical reactivity following photoionization in liquid

The ultrafast dynamics of the cationic hole formed in bulk liquid water following ionization is investigated by ab initio molecular dynamics simulations and an experimentally accessible signature is suggested that might be tracked by femtosecond pump-probe spectroscopy. This is one of the fastest fundamental processes occurring in radiation-induced chemistry in aqueous systems and biological tissue. However, unlike the excess electron formed in the same process, the nature and time evolution of the cationic hole has been hitherto little studied. Simulations show that an initially partially delocalized cationic hole localizes within ∼30 fs after which proton transfer to a neighboring water molecule proceeds practically immediately, leading to the formation of the OH radical and the hydronium cation in a reaction which can be formally written as The exact amount of initial spin delocalization is, however, somewhat method dependent, being realistically described by approximate density functional theory methods corrected for the self-interaction error. Localization, and then the evolving separation of spin and charge, changes the electronic structure of the radical center. This is manifested in the spectrum of electronic excitations which is calculated for the ensemble of ab initio molecular dynamics trajectories using a quantum mechanics/molecular mechanics (QM/MM) formalism applying the equation of motion coupled-clusters method to the radical core. A clear spectroscopic signature is predicted by the theoretical model: as the hole transforms into a hydroxyl radical, a transient electronic absorption in the visible shifts to the blue, growing toward the near ultraviolet. Experimental evidence for this primary radiation-induced process is sought using femtosecond photoionization of liquid water excited with two photons at 11 eV. Transient absorption measurements carried out with ∼40 fs time resolution and broadband spectral probing across the near-UV and visible are presented and direct comparisons with the theoretical simulations are made. Within the sensitivity and time resolution of the current measurement, a matching spectral signature is not detected. This result is used to place an upper limit on the absorption strength and/or lifetime of the localized H 2 O + (aq) species

Editor's Choice-2017 ESC Guidelines on the Diagnosis and Treatment of Peripheral Arterial Diseases, in collaboration with the European Society for Vascular Surgery (ESVS)

Document covering atherosclerotic disease of extracranial carotid and vertebral, mesenteric, renal, upper and lower extremity arteries Endorsed by: the European Stroke Organization (ESO) The Task Force for the Diagnosis and Treatment of Peripheral Arterial Diseases of the European Society of Cardiology (ESC) and of the European Society for Vascular Surgery (ESVS) Authors/Task Force Members (a), Victor Aboyans (*), Jean- Baptiste Ricco (*), Marie- Louise E. L. Bartelink, Martin Bjorck, Marianne Brodmann, Tina Cohnert, Jean-Philippe Collet, Martin Czerny, Marco De Carlo, Sebastian Debus, Christine Espinola-Klein, Thomas Kahan, Serge Kownator, Lucia Mazzolai, A. Ross Naylor, Marco Roffi, Joachim Rother, Muriel Sprynger, Michal Tendera, Gunnar Tepe, Maarit Venermo, Charalambos Vlachopoulos, Ileana Desormais Document Reviewers (b), Petr Widimsky, Philippe Kolh, Stefan Agewall, Hector Bueno, Antonio Coca, Gert J. De Borst, Victoria Delgado, Florian Dick, Cetin Erol, Marc Ferrini, Stavros Kakkos, Hugo A. Katus, Juhani Knuuti, Jes Lindholt, Heinrich Mattle, Piotr Pieniazek, Massimo Francesco Piepoli, Dierk Scheinert, Horst Sievert, Iain Simpson, Jakub Sulzenko, Juan Tamargo, Lale Tokgozoglu, Adam Torbicki, Nikolaos Tsakountakis, Jose Tunon, Melina Vega de Ceniga, Stephan Windecker, Jose Luis ZamoranoPeer reviewe

Benchmark full configuration interaction and equation-of-motion coupled-cluster model with single and double substitutions for ionized systems results for prototypical charge transfer systems: Noncovalent ionized dimers

© 2007 American Institute of Physics. The electronic version of this article is the complete one and can be found at: http://dx.doi.org/10.1063/1.2795709DOI: 10.1063/1.2795709Benchmark full configuration interaction and equation-of-motion coupled-cluster model with single and double substitutions for ionized systems EOM-IP-CCSD results are presented for prototypical charge transfer species. EOM-IP-CCSD describes these doublet systems based on the closed-shell reference and thus avoids the doublet instability problem. The studied quantities are associated with the quality of the potential energy surface PES along the charge transfer coordinate and distribution of the charge between fragments. It is found that EOM-IP-CCSD is capable of describing accurately both the charge-localized and charge-delocalized systems, yielding accurate charge distributions and energies. This is in stark contrast with the methods based on the open-shell reference, which overlocalize the charge and produce a PES cusp when the fragments are indistinguishable

Dynamics of Water Confined in Reversed Micelles:Multidimensional Vibrational Spectroscopy Study

<p>Here we perform a comprehensive study of ultrafast molecular and vibrational dynamics of water confined in small reversed micelles (RMs). The molecular picture is elucidated with two-dimensional infrared (2D IR) spectroscopy of water OH stretch vibrations and molecular dynamics simulations, bridged by theoretical calculations of linear and 2D IR vibrational spectra. To investigate the effects of intermolecular coupling, experiments and modeling are performed for isotopically diluted (HDO in D2O) and undiluted (H2O) water. We put a separation of water inside RMs into two subensembles (water-bound and surfactant-bound molecules), observed by many before, on a solid theoretical basis. Water molecules fully attached to the lipid interface ("shell" water) are decoupled from one another and from the central water nanopool ("core" water). The environmental fluctuations are largely "frozen" for the shell water, while the core waters demonstrate much faster dynamics but still not as fast as in the bulk case. A substantial nanoconfinement effect on the dynamics of the core water is observed after disentanglement of the shell water contribution, which is fully confirmed by the simulations of 2D IR spectra. Current results provide new insights into interaction between biological objects like membranes or proteins with the surrounding aqueous bath, and highlight peculiarities in vibrational energy redistribution near the lipid surface.</p>

Hydrogen bonding at the water surface revealed by isotopic dilution spectroscopy. Nature 474

The air-water interface is perhaps the most common liquid interface. It covers more than 70 per cent of the Earth&apos;s surface and strongly affects atmospheric, aerosol and environmental chemistry. The airwater interface has also attracted much interest as a model system that allows rigorous tests of theory, with one fundamental question being just how thin it is. Theoretical studies have suggested a surprisingly short &apos;healing length&apos; of about 3 ångströms (1 Å 5 0.1 nm), with the bulk-phase properties of water recovered within the top few monolayers The vibrational spectroscopy of aqueous interfaces has progressed significantly in recent years with the development of surface-selective spectroscopic techniques The intramolecular and intermolecular vibrational coupling between the OH transition dipoles of the same molecule or between neighbours affect the spectral lineshapes of the water OH-stretch band We overcome these challenges by using the heterodyne-detected SFG technique 10 , which uses interference of the signal with a reference beam to (1) amplify the SFG signal, considerably enhancing the sensitivity, (2) make it linear with the number of chromophores, an