The Dynamics of Aqueous Hydroxide Ion Transport Probed via Ultrafast Vibrational Echo Experiments

Paper presented at the Sixteenth International Conference on Ultrafast Phenomena.We use peakshift, transient grating, and 2D IR measurements to probe the dynamics of NaOD solutions. Our experiments suggest that OD- possesses a stable solvation shell and signatures of fast intermolecular proton transfer are observed

Interchain effects in the ultrafast photophysics of a semiconducting polymer: THz time-domain spectroscopy of thin films and isolated chains in solution

Euan Hendry, Mattijs Koeberg, Juleon M. Schins, H. K. Nienhuys, V. Sundström, L. D. A. Siebbeles, and Mischa Bonn, Physical Review B, Vol. 71, article 125201 (2005). "Copyright © 2005 by the American Physical Society."We compare the generation and decay dynamics of charges and excitons in a model polymer semiconductor (MEH-PPV) in solution and drop-cast thin films, by recording the sub-ps transient complex conductivity using THz time-domain spectroscopy. The results show that the quantum efficiency of charge generation is two orders of magnitude smaller in solution (~10–5) than in the solid film (~10–3). The proximity of neighboring chains in the films apparently facilitates (hot) exciton dissociation, presumably by allowing the electron and hole to separate on different polymer strands. For both samples, photoexcitation leads to the predominant formation of bound charge pairs (excitons) that can be detected through their polarizability. Surprisingly, the polarizability per absorbed photon is a factor of 3 larger in solution than in the film, suggesting that interchain interactions in the film do not result in a substantial delocalization of the exciton wave function

Experimental study of EUV mirror radiation damage resistance under long term free electron laser exposures below the single shot damage threshold

The durability of grazing and normal incidence optical coatings has been experimentally assessed under free electron laser irradiation at various numbers of pulses up to 16 million shots and various fluence levels below 10 of the single shot damage threshold. The experiment was performed at FLASH, the Free electron LASer in Hamburg, using 13.5 nm extreme UV EUV radiation with 100 fs pulse duration. Polycrystalline ruthenium and amorphous carbon 50 nm thin films on silicon substrates were tested at total external reflection angles of 20 and 10 grazing incidence, respectively. Mo Si periodical multilayer structures were tested in the Bragg reflection condition at 16 off normal angle of incidence. The exposed areas were analysed post mortem using differential contrast visible light microscopy, EUV reflectivity mapping and scanning X ray photoelectron spectroscopy. The analysis revealed that Ru and Mo Si coatings exposed to the highest dose and fluence level show a few per cent drop in their EUV reflectivity, which is explained by EUV induced oxidation of the surfac

Mechanism of single shot damage of Ru thin films irradiated by femtosecond extreme UV free electron laser

Ruthenium is a perspective material to be used for XUV mirrors at free electron laser facilities. Yet, it is still poorly studied in the context of ultrafast laser matter interaction. In this work, we present single shot damage studies of thin Ru films irradiated by femtosecond XUV free electron laser pulses at FLASH. Ex situ analysis of the damaged spots, performed by different types of microscopy, shows that the weakest detected damage is surface roughening. For higher fluences we observe ablation of Ru. Combined simulations using Monte Carlo code XCASCADE 3D and the two temperature model reveal that the damage mechanism is photomechanical spallation, similar to the case of irradiating the target with optical lasers. The analogy with the optical damage studies enables us to explain the observed damage morphologie

Orientational relaxation of liquid water molecules as an activated process

Femtosecond mid-infrared pump-probe spectroscopy is used to study the orientational relaxation of HDO molecules dissolved in liquid D2O. In this technique, the excitation of the O-H stretch vibration is used as a label in order to follow the orientational motion of the HDO molecules. The decay of the anisotropy is nonexponential with a typical time scale of 1 ps and can be described with a model in which the reorientation time depends on frequency and in which the previously observed spectral diffusion is incorporated. From the frequency and temperature dependence of the anisotropy decay, the activation energy for reorientation can be derived. This activation energy is found to increase with increasing hydrogen bond strength. (C) 2000 American Institute of Physics. [S0021-9606(00)52019- 4

Dynamics of water molecules in an alkaline environment

We report on a two-color mid-infrared pump-probe spectroscopic study of the dynamics of the OH stretch vibrations of HDO molecules dissolved in a concentrated (10 M) solution of NaOD in D2O. We observe that spectral holes can be created in the broad OH stretch absorption band that change neither position nor width on a picosecond time scale. This behavior differs strongly from that of pure HDO:D2O where rapid spectral diffusion (tau(c)approximate to600 fs) occurs. The long-living inhomogeneity indicates that a concentrated aqueous NaOX (X=H,D) solution has a very static hydrogen-bond network. The results also show that the absorption band of the OH stretch vibration consists of two separate classes of OH groups with very different vibrational lifetimes. For component I, the lifetime of the OH stretch vibration is similar to600 fs and increases with OH frequency, which can be explained from the accompanying decrease in the strength of the hydrogen-bond interaction. This component represents HDO molecules of which the OH group is bonded to a D2O molecule via a DO-H.OD2 hydrogen bond. For component II, the lifetime is similar to160 fs, and does not show a significant frequency dependence. This component represents HDO molecules that are hydrogen bonded to a D2O molecule or an OD- ion. The short, frequency-independent vibrational lifetime of component II can be explained from the participation of the HDO molecule and its hydrogen-bonded partner in deuteron and/or proton-transfer processes. (C) 2002 American Institute of Physic

Generation of mid-infrared pulses by X(3) difference frequency generation in CaF2 and BaF2

Tunable mid-IR pulses in the range 1300-4200 cm(-1) (7.7-2.4 mum) are generated through a phase-matched four-wave mixing process in ordinary mid-IR window materials such as CaF2 and BaF2. In this process the difference frequency nu (3) = 2 nu (2) - nu (1) is generated from pump fields nu (1) and nu (2). The process can be phase matched to different frequencies by adjustment of the angle between the pump fields. (C) 2001 Optical Society of Americ

Mechanism for vibrational relaxation in water investigated by femtosecond infrared spectroscopy

We present a study on the relaxation of the O¿H stretch vibration in a dilute HDO:D2O solution using femtosecond mid-infrared pump-probe spectroscopy. We performed one-color experiments in which the 01 vibrational transition is probed at different frequencies, and two-color experiments in which the 12 transition is probed. In the one-color experiments, it is observed that the relaxation is faster at the blue side than at the center of the absorption band. Furthermore, it is observed that the vibrational relaxation time T1 shows an anomalous temperature dependence and increases from 0.74 ± 0.01 ps at 298 K to 0.90 ± 0.02 ps at 363 K. These results indicate that the O¿HO hydrogen bond forms the dominant accepting mode in the vibrational relaxation of the O¿H stretch vibration. ©1999 American Institute of Physics

Transient absorption of vibrationally excited water

International audienc