Implementation of room temperature femtosecond echo-processing

Conditions for implementing room temperature femtosecond echo-processing in a phtalocyanine-doped polyvinylbutyral film were studied. A logical operation of bit-by-bit multiplication on the basis of the nonlinear third-order optical response (primary photon echo) of the medium was performed in a time of less than 1 ps.     

Probing solute-solvent interaction in 1-ethyl-3-methylimidazolium-based room temperature ionic liquids: A time-resolved fluorescence anisotropy study

Rotational diffusion of two organic solutes, coumarin153 (C153) and 4-aminophthalimide (AP) has been investigated in four ionic liquids (ILs), viz. 1-ethyl-3-methylimidazolium trifluoroacetate (EMIMTFA), 1-ethyl-3-methylimidazolium ethylsulfate (EMIMESU), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMTFB) and 1-ethyl-3-methylimidazolium tetracyanoborate (EMIMTCB), as a function of temperature. Between the two probes, AP can act as hydrogen-bond-donor to the solvents having hydrogen bond acceptor ability. The results indicate that the rotational dynamics of C153 is mainly governed by the viscosity of the medium. On the other hand, the rotational motion of AP is found to be significantly hindered in the ILs depending on the nature of anions of the ILs. Rotational coupling constant values for AP in the ILs follow the order TFA?>?ESU?>?TCB?>?TFB. The slower rotational motion of AP in these ILs has been attributed to the specific hydrogen bonding interaction between AP and anions of ILs.

Hydrogen diffusion in titanium at room temperature

The diffusion of hydrogen in technically pure VT1-00 titanium is studied at room temperature under conditions of hydrogen penetration from a glow discharge plasma. Hydrogen penetration occurs under conditions of hydride phase growth. The diffusion coefficients of hydrogen in titanium at room temperature are estimated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 43–47, March, 1982.     

Studies on electrowetting of room temperature ionic liquids

This paper reports experimental investigations on the electrowetting behavior of ionic liquids in comparison with aqueous electrolytes, which is one of the important research topics in optofluidics. The effect of applied voltage on the contact angle is reported in detail. In addition, the liquid–solid material interfacial tension and the thickness of insulating layer are estimated under certain conditions. Related conclusions are valuable in the field of future electrowetting applications.     

Intensity-independent molecular rotational decoherence lifetimes measured with mean wavelength shifts of femtosecond pulses

We report on an experimental investigation on the dynamic decoherence process of molecular rotational wavepackets during femtosecond laser filamentation based on time-dependent mean wavelength shifts of a weak probe pulse. Details of periodic revival structures of transient alignment can be readily obtained from the measured shifted spectra due to the periodic modulation of the molecular refractive index. Using the method, we measured decoherence lifetimes of molecular rotational wavepackets in N_2 and O_2 under different experimental conditions. Our results indicate that decoherence lifetimes of molecular rotational wavepackets are primarily determined by the relative population of rotational states in the wave packet and intermolecular collisions,rather than the focusing intensity.     

The electrochemistry of arylated anthraquinones in room temperature ionic liquids

Arylated anthraquinone derivatives of different sizes and different π‐basicities have been prepared, and the electrochemical behaviour of these substances has been studied on screen printed graphite electrodes in the three room temperature ionic liquids (RTILs), 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([C₄MIM][PF₆]), 1‐hexyl‐3‐methylimidazolium hexafluorophosphate ([C₆MIM][PF₆]) and 1‐octyl‐3‐methylimidazolium hexafluorophosphate ([C₈MIM][PF₆]). Half redox potentials for the first and second one electron reduction waves were identified, and the diffusion coefficient values were estimated from cyclic voltammetry measurements. The influence of the nature of the RTIL and of the substitution pattern of the anthraquinone on the solvodynamic radii were studied. A correlation of the reductive potentials with the corresponding Hammett constants of the substituents was tested. Copyright © 2013 John Wiley & Sons, Ltd.     

The influence of molecular rotational diffusion on Gaussian pulse-induced third-order electric polarisation in liquids

Time evolution curves of the changes in nonlinear electric polarisation induced by Gaussian pulses are calculated theoretically with the Smoluchowski-Debye molecular rotational diffusion equation not including the influence of the moment of inertia of the molecules or their interactions. Graphs show the dynamics of the third-order electric polarisation versus the Gaussian pulse width and the parameter R, defining the balance between the dipolar and anisotropically polarisable properties of the molecules.     

Nonstationary diffusion in a multiphase medium

The process of nonstationary diffusion of matter in a multiphase medium with sharp steps of the diffusion coefficient and an arbitrary number of phases is considered. The boundary conditions at the points of phase separation are determined. An exact solution is obtained, and the nonstationary concentration of matter is shown to be described by an infinite superposition of time-dependent Gaussian curves. Some examples are proposed and the results obtained are interpreted physically.State University, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, Nos. 1–2, pp. 56–68, January–February, 1995.     

Entangled femtosecond free induction signals in a cadmium sulfide crystal at room temperature

Entangled free induction decay (EFID) femtosecond signals are experimentally observed for the first time at a wavelength of 790 nm in a cadmium sulfide (CdS) crystal in the two-photon absorption (TPA) regime upon excitation by two crossed (angle, 60°) laser beams. The sample emitted two EFID signals simultaneously in opposite directions. The signals were diffracted by nonequilibrium electric polarization gratings induced by two laser beams in accordance with the laws of energy and momentum conservation. The possibility of exciting EFID signals in the three-photon absorption regime is discussed.     

Multipoles and rotational relaxation in liquids

The role of multipolar interactions in quenching free rotation in condensed phases is discussed, with particular attention paid to the HCl-SF₆ system. The magnitude of these interactions is shown to be closely correlated with the dielectric loss of the solvent, and to be sufficient to explain at least partially the variations of linewidth in the HCl rotational spectrum.     

Shear induced anisotropy in two-dimensional liquids

The behavior of a dense two-dimensional soft disc liquid under shear is studied via nonequilibrium molecular dynamics. The structure factor for the liquid at a given shear rate is evaluated directly by plotting the particle positions, taken at random from the NEMD simulation at that shear, onto photographic film and using light scattering to obtain a diffraction pattern. The pair correlation function of this system is also extracted directly by histogramming the particle positions with respect to a given central particle as a function of separation and angle. The pair correlation function is compared to that approximated by a Fourier series expansion to rank ten. Results are reported as a function of shear rate from a shear rate of 0.1 (when the fluid is essentially Newtonian) to 10 (when the fluid can display a string phase). The appearance of the string phase is discussed and shown to be a consequence of the definition of temperature in the simulation algorithm. A modification of the algorithm is proposed. Comparisons between this work and previous work with three-dimensional liquids are given. The two-dimensional structure factor is compared with that obtained from a real colloidal suspension via light scattering.     

Polarization anisotropy in room temperature contactless electroreflectance spectrum of self-organized lateral compositional superlattices

We report the results of room temperature contactless electroreflectance measurements on (GaP)₂(InP)₂superlattices grown on GaAs (001) substrates which show lateral composition modulation along the [110] direction in the (001) plane. The strong polarization anisotropy of some features in the spectrum has been explained by identifying them as arising from transitions in the lateral superlattice formed due to the composition modulation. The measured optical transition energies are considerably lower than theoretical estimates based on the random alloy model, suggesting the need for a better model to describe the electronic band structure of this system.     

Unusual aspects of ion‐pairing effects in room temperature ionic liquids

Herein, we report our observations on voltammetric investigations about the redox behaviour of para‐nitrotoluene, 1,4‐benzoquinone and ferrocene, aimed at exploring the unusual aspects of ion‐pairing phenomena in imidazolium‐based room temperature ionic liquids (RTILs). Our observations indicate that the stabilization of electrogenerated ion/radical ion intermediates depends upon the potential of the working electrode and the overall composition of RTILs. In light of observed relative trends and quantum mechanical calculations, we propose that the ion‐pair stabilization of electrogenerated charged species in RTILs is closely related to the structural organization and composition of electrode/RTIL interface. Copyright © 2012 John Wiley & Sons, Ltd.     

Electroreduction of N-methylphthalimide in room temperature ionic liquids under insonated and silent conditions

The selective electroreduction N-methylphthalimide to 3-hydroxy-2-methyl-isoindolin-1-one has been performed in ionic liquids using phenol as a proton donor under silent and ultrasonic conditions. A significant increase in the rate of electroreduction is shown using ultrasonic activation and in addition high current efficiencies were observed. Some decomposition of the ionic liquid was found to have occurred under exposure to ultrasound.     

Artifacts in femtosecond transient absorption spectroscopy

The paper discusses three different artifacts related to two-photon absorption (TPA), stimulated Raman amplification (SRA) and cross-phase modulation (XPM), all intrinsic to transient absorption measurements with femtosecond time resolution. Certain properties of these signals are analysed and shown to superimpose onto measured transient absorption spectra. Ways of reducing the influence of the artifacts discussed are suggested. A simple correcting procedure based on the linear intensity dependence of the artifacts discussed is proposed. Received: 29 May 2001 / Final version: 15 October 2001 / Published online: 29 November 2001     

Measuring the solubility of benzoic acid in room temperature ionic liquids using chronoamperometric techniques

The electrochemical reduction of benzoic acid (BZA) has been studied at platinum micro‐electrodes (10 and 2 µm diameters) in acetonitrile (MeCN) and six room temperature ionic liquids (RTILs): [C₂mim][NTf₂], [C₄mim][NTf₂], [C₄mpyrr][NTf₂], [C₄mim][BF₄], [C₄mim][NO₃] and [C₄mim][PF₆] (where [C_nmim]⁺ = 1‐alkyl‐3‐methylimidazolium, [NTf₂]^? = bis(trifluoromethylsulphonyl)imide, [C₄mpyrr]⁺ = N‐butyl‐N‐methylpyrrolidinium, [BF₄]^? = tetrafluoroborate, [NO₃]^? = nitrate and [PF₆]^? = hexafluorophosphate). Based on the theoretical fitting to experimental chronoamperometric transients in [C₄mpyrr][NTf₂] and MeCN at several concentrations and on different size electrodes, it is suggested that a fast chemical step preceeds the electron transfer step in a CE mechanism (given below) in both RTILs and MeCN, leading to the appearance of a simple one‐electron transfer mechanism. The six RTIL solvents and MeCN were saturated with BZA, and potential‐step chronoamperometry revealed diffusion coefficients of 170, 4.6, 3.2, 2.7, 1.8, 0.26 and 0.96 × 10^?11 m² s^?1 and solubilities of 850, 75, 78, 74, 220, 2850 and 48 mM in MeCN and the six ionic liquids, respectively, at 298 K. The high solubility of BZA in [C₄mim][NO₃] may suggest a strong interaction of the dissolved proton with the nitrate anion. Although there are relatively few literature reports of solubilities of organic solutes in RTILs at present, these results suggest the need for further studies on the solubilities of organic species (particularly acids) in RTILs, because of the contrasting interaction of dissolved species with the RTIL ions. Chronoamperometry is suggested as a convenient methodology for this purpose. Copyright © 2008 John Wiley & Sons, Ltd.     

Tracer diffusion in glassforming liquids

In the last decades, a wide collection of experimental evidence has been found in the study of supercooled glassformers on the existence of a crossover between two dynamical regimes at a temperature T_c. We discuss the validity of the Vogel-Fulcher-Tammann in both regions. The breakdown of the Stokes-Einstein relation below T_c is presented, indicating that the diffusion coefficient of a tracer becomes decoupled from the viscosity through an exponent ξ, and the diffusion process is intensified. We verify that a temperature shift on the diffusion coefficient introduces the same effect as the Stokes-Einstein breakdown equation. We present the dependence of this exponent on the ratio between the radii of the tracer and the host liquid molecule.