Femtosecond Pulse Radiolysis Research Articles

Femtosecond Pulse Radiolysis

SUMMARYFemtosecond pulse radiolysis has been developed in order to study reactions induced in materials by an electron beam. The femtosecond electron pulse is generated by optimizing the laser photocathode FR electron gun accelerator. A time resolution of 240 fs was achieved by using a femtosecond electron pulse, and the formation of hydrated electrons was observed under femtosecond pulse radiolysis. In order to improve the time resolution of the pulse radiolysis, the equivalent velocity spectroscopy (EVS) method is essential for avoiding degradation in the time resolution caused by velocity differences between the electrons and light in a sample.

Examination of the formation process of pre-solvated and solvated electron in n-alcohol using femtosecond pulse radiolysis

Abstract The formation process of pre-solvated and solvated electron in methanol (MeOH), ethanol (EtOH), n -butanol (BuOH), and n -octanol (OcOH) were investigated using a fs-pulse radiolysis technique by observing the pre-solvated electron at 1400 nm. The formation time constants of the pre-solvated electrons were determined to be 1.2, 2.2, 3.1, and 6.3 ps for MeOH, EtOH, BuOH, and OcOH, respectively. The formation time constants of the solvated electrons were determined to be 6.7, 13.6, 22.2, and 32.9 ps for MeOH, EtOH, BuOH, and OcOH, respectively. The formation dynamics and structure of the pre-solvated and solvated electrons in n -alcohols were discussed based on relation between the obtained time constant and dielectric relaxation time constant from the view point of kinetics. The observed formation time constants of the solvated electrons seemed to be strongly correlated with the second component of the dielectric relaxation time constants, which are related to single molecule motion. On the other hand, the observed formation time constants of the pre-solvated electrons seemed to be strongly correlated with the third component of the dielectric relaxation time constants, which are related to dynamics of hydrogen bonds.

Femtosecond Pulse Radiolysis

Femtosecond pulse radiolysis has been developed in order to study reactions induced in materials by an electron beam. The femtosecond electron pulse is generated by optimizing the laser photocathode FR electron gun accelerator. A time resolution of 240 fs was achieved by using a femtosecond electron pulse, and the formation of hydrated electrons was observed under femtosecond pulse radiolysis. In order to improve the time resolution of the pulse radiolysis, the equivalent velocity spectroscopy EVS method is essential for avoiding degradation in the time resolution caused by velocity differences between the electrons and light in a sample.

Femtosecond pulse radiolysis study of geminate ion recombination in biphenyl–dodecane solution

The kinetics of geminate ion recombination was studied by the femtosecond pulse radiolysis of n-dodecane with biphenyl solution. The complicated biphenyl concentration-dependence behaviors of the transient absorptions at 800nm are observed and elucidated with a Monte Carlo simulation of geminate recombination and charge transfer processes in the biphenyl-dodecane solution. The experimental data suggested the existence of n-dodecane excited radical cation in the radiolysis. It plays very important roles especially in the high-concentration solution. The reaction rate constant of the excited radical cation with biphenyl molecule was 3.5×1011dm3mol−1s−1, which is comparable with the reaction rate constant of the electron with biphenyl molecule. The contributions of the geminate ion recombination, the charge transfer reaction and the relaxation of the excited radical cation were obtained as a function of the biphenyl concentration.

Femtosecond pulse radiolysis study on geminate ion recombination in n-dodecane

The primary process of radiation chemistry was studied by the femtosecond pulse radiolysis in n-dodecane. The time-dependent behavior of geminate ion recombination in n-dodecane was investigated in neat n-dodecane and the solutions containing electron and cation scavengers. The excited radical cation was found from analyzing the geminate process by the theoretical simulation based on the diffusion theory. The life time of the excited radical cation was 7 ps in n-dodecane. The reaction rate constant of the excited radical cation with the triethylamine (TEA) was 3.3×10 11 dm 3 mol −1 s −1, which is one order higher than the normal diffusion rate constant. Although 74% of the excited radical cations are relaxed to the radical cation, the residual 26% are geminately recombined with electrons.

Simulation study of sub-femtosecond electron bunch generation using photocathode RF gun linac

Pulse radiolysis, a stroboscopic method involving the use of an ultrashort electron bunch and ultrashort light, is essential for the observation of ultrafast reactions. The time resolution of pulse radiolysis depends on the electron bunch length. At Osaka University, a 98-fs electron bunch was generated using a photocathode RF gun linac for the development of femtosecond pulse radiolysis. In order to improve the time resolution of pulse radiolysis, the feasibility of sub-femtosecond electron bunch generation using a photocathode RF gun linac and a magnetic bunch compressor was studied in a simulation. Increase in bunch length due to higher-order effects and bunch charge was investigated using the simulation codes PARMELA and ELEGANT.

Femtosecond pulse radiolysis and femtosecond electron diffraction

A femtosecond pulse radiolysis with a time resolution of 210 fs has been developed by using a femtosecond electron beam and a femtosecond laser light. It has successfully opened the study of ultra-fast reactions or phenomena in materials—the first observation of the femtosecond formation process of the hydrated electron in water pulse radiolysis. The use of a photocathode femtosecond electron gun, which produces a near-relativistic 100 fs electron beam, has been approached to construct femtosecond megavolt electron diffraction. The dependencies of the emittance, bunch length, and energy spread on the radio-frequency (rf) and space-charge effects in the rf gun have been investigated.

Light-Induced Temperature Jump Causes Power-Dependent Ultrafast Kinetics of Electrons Generated in Multiphoton Ionization of Liquid Water

Picosecond geminate recombination kinetics for electrons generated by multiphoton ionization of liquid water become power dependent when the radiance of the excitation light is greater than 0.3-0.5 TW/cm^2 (the terawatt regime). To elucidate the mechanism of this power dependence, tri- 400 nm photon ionization of water has been studied using pump-probe laser spectroscopy on the pico- and femtosecond time scales. We suggest that the observed kinetic transformations are caused by a rapid temperature jump in the sample. Such a jump is inherent to multiphoton ionization in the terawatt regime, when the absorption of the pump light along the optical path becomes very nonuniform. The heating of water is substantial (tens of degrees C) because the 3-photon quantum yield of the ionization is relatively low, ca. 0.42, and a large fraction of the excitation energy is released into the solvent bulk as heat. Evidence of the temperature jump is the observation of a red shift in the absorption spectrum of (thermalized) electron and by characteristic "flattening" of the thermalization dynamics in the near infra-red. The temperature jump in the terawatt regime might be ubiquitous in multiphoton ionization in molecular liquids. The implications of these observations for femtosecond pulse radiolysis of water are discussed.