Radiolysis picosecond pulse

The electron itself is frequently used as a primary source of radiation, various kinds of accelerators being available for that purpose. Particularly important are pulsed electron sources, such as the nanosecond and picosecond pulse radiolysis machines, which allow very fast radiation-induced reactions to be studied (Tabata et al, 1991). Note that secondary electron radiation always constitutes a significant part of energy transferred by heavy charged particles. For these reasons, the electron occupies a central role in radiation chemistry. 

With the advent of picosecond-pulse radiolysis and laser technologies, it has been possible to study geminate-ion recombination (Jonah et al, 1979 Sauer and Jonah, 1980 Tagawa et al 1982a, b) and subsequently electron-ion recombination (Katsumura et al, 1982 Tagawa et al, 1983 Jonah, 1983) in hydrocarbon liquids. Using cyclohexane solutions of 9,10-diphenylanthracene (DPA) and p-terphenyl (PT), Jonah et al. (1979) observed light emission from the first excited state of the solutes, interpreted in terms of solute cation-anion recombination. In the early work of Sauer and Jonah (1980), the kinetics of solute excited state formation was studied in cyclohexane solutions of DPA and PT, and some inconsistency with respect to the solution of the diffusion equation was noted.1... 

With the development of the picosecond pulse radiolysis, the kinetics data of the geminate ion recombination have been directly obtained. The history of picosecond and subpicosecond pulse radiolysis is shown in Fig. 7. Very recently, the first construction of the femtosecond pulse radiolysis and the improvement of the subpicosecond pulse radiolysis started in Osaka University. 

The first picosecond pulse radiolysis experiment was carried out in the late 1960s by the so-called stroboscopic method (generally pomp and probe method) at University of... 

Now several picosecond pulse radiolysis systems are operating in Argonne National Laboratory, Brookhaven National Laboratory and University of Tokyo and are under construction in University of Paris South and Waseda University, although only one sub-picopulse radiolysis is operating in Osaka University. 

Reactions of e. It is convenient to consider these reactions here. That the electron can react with solutes before it becomes solvated is clearly demonstrated by the data in Fig. 3, which were obtained by picosecond pulse radiolysis [31]. The data show that there is no good correlation between the C37 value of a solute and its rate constant k for reaction with measured at the same high concentrations of solute used to determine C37. The parameter C37 is the concentration of solute that lowers the earliest measurable value of G(gaq) to 37% of the value obtained in the absence of solute. A linear correlation between C37 and k would be expected if the solute merely reacted with e before this earliest time of... 

Details of the picosecond pulse radiolysis system for emission (7) and absorption (8) spectroscopies with response time of 20 and 60 ps, respectively, including a specially designed linear accelerator (9) and very fast response optical detection system have been reported previously. The typical pulse radiolysis systems are shown in Figures 1 and 2. The detection system for emission spectroscopy is composed of a streak camera (C979, HTV), a SIT... 

Figure 1. The schematic diagram of the picosecond pulse radiolysis system for emission spectroscopy.

Other probes of the initial distribution have been tried. A few studies of the time-dependent ion-pair recombination probability have been made recently with picosecond pulse radiolysis equipment. A magnetic field alters the rate of interconversion between a triplet and singlet ion-pair. If this rate is fast enough to compete with the recombination rate of ions, the yield of recombined ion-pairs is markedly affected by the magnetic field. 

After thermalization, the electron may recombine with a positive ion or be captured by a molecule forming a negative ion, or it may be locked in a trap the role of which may be played by fluctuation cavities or structural disturbances in the medium, or by polarization pits that the electron digs when it interacts with surrounding molecules. Such captured electrons are called solvated electrons (in water they are sometimes called hydrated electrons).31,32 According to the data obtained in picosecond pulsed-radiolysis sets,33 34 the solvation time of an electron is 2 x 10-12 s in water and —10 11 s in methanol. 

As has already been mentioned, picosecond pulsed radiolysis offers great possibilities for studying the short-lived transient processes. In Ref. 326 the solutions of 2,5-diphenyloxazol (DPO) in different solvents were irradiated by picosecond electron pulses obtained from an accelerator. The authors have found two types of excitations of DPO, which they have named the fast and the slow excitations. With fast excitation the luminescence appears during the electron pulse and stops growing at the end of the pulse, after 10 ps. With slow excitation the luminescence is formed within 1 ns. At small DPO concentrations the observed intensity of fast luminescence cannot be explained by direct excitation by electrons (cf. data of Ref. 325). Analyzing the results of experiments with different solvents and different types of additives, Katsumura et al.326 conclude that the main part of the fast luminescence of DPO is due to VCR absorption. 

Wolff RK, Bronskill MJ, Hunt JW (1973) Picosecond pulse radiolysis. IV. Yield of the solvated electron at 30 picoseconds. J Phys Chem 77 1350-1355... 

Katsumura, Y., Yoshida, Y., Tagawa, S., Tabata, Y. 1983. Study on the excited state of liquid alkanes and energy transfer process by means of picosecond pulse radiolysis. Radiat. Phys. Chem. 21(1-2) 103-111. 

Yoshida, Y., Ueda, T., Kobayashi, H., Tagawa, S. 1993. Studies of geminate ion recombination and formation of excited states in liquid n-dodecane by means of a new picosecond pulse radiolysis system. Nucl. Instr. Meth. Phys. Res. A 327 41 —43. 

Polyvinylcarbazole exhibits excimer emission from the carbazole unit. By use of picosecond pulse radiolysis, Tagawa et al. (1979) showed that excitation produces two excimers, the normal sandwich excimer which fluoresces at 420 nm and another which fluoresces at 375 nm. The latter high energy species decays to the lower energy species very quickly and therefore good time resolution is necessary in order to see both. 

Lam KY, Himt JW. (1975) Picosecond pulse radiolysis. VI. Fast electron reactions in concentrated solutions of scavengers in water and alcohols. Int J Radiat Phys Chem 7 317-338. 

Wishart JF, Cook AR, Miller JR. (2004) The LEAF picosecond pulse radiolysis facility at Brookhaven National Laboratory. Rev Sci Inst 75 4359 366. 

The construction of the first picosecond pulse radiolysis facilities enabled pioneering investigations of the elementary processes mentioned... 

Table 1. Comparison of specifications of photocathode electron gun accelerators for picosecond pulse radiolysis.

The overall time resolution 8t of a picosecond pulse radiolysis detection system is approximately expressed as ... 

Table 2. Comparison between time-resolved spectrophotometric detection set-ups of several laser-photocathode electron accelerator facilities for picosecond pulse radiolysis. 

Yoshida Y, Mizutani Y, Kozawa T, Saeki A, Seki S, Tagawa S, Ushida K. (2001) Development of laser-synchronized picosecond pulse radiolysis system. Radiat Phys Chem 60 313-318. 

Saeki A, Kozawa T, Tagawa S. (2006) Picosecond pulse radiolysis using femtosecond white light with a high S/N spectrum acquisition system in one beam shot. Nucl Instrum Meth A 556 391-396. 

Yang J, Kondoh T, Norizawa K, Nagaishi R, Tagushi M, Takahashi K, Rat oh R, Anishchik SV, Yoshida Y, Tagawa S. (2008) Picosecond pulse radiolysis Dynamics of solvated electrons in ionic liquid and geminate ion recombination in liquid alkanes. Radiat Phys Chem 77 1233-1238. 

Baldacchino G, De Waele V, Monard H, Sorgues S, Gobert F, Larbre J-P, Vigneron G, Marignier J-L, Pommeret S, Mostafavi M. (2006) Hydrated electron decay measurements with picosecond pulse radiolysis at elevated temperature up to 350°C. Chem Phys Lett A2A 77-81. 

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