Pulse irradiation

With M = He, experimeuts were carried out between 255 K aud 273 K with a few millibar NO2 at total pressures between 300 mbar aud 200 bar. Temperature jumps on the order of 1 K were effected by pulsed irradiation (< 1 pS) with a CO2 laser at 9.2- 9.6pm aud with SiF or perfluorocyclobutaue as primary IR absorbers (< 1 mbar). Under these conditions, the dissociation of N2O4 occurs within the irradiated volume on a time scale of a few hundred microseconds. NO2 aud N2O4 were monitored simultaneously by recording the time-dependent UV absorption signal at 420 run aud 253 run, respectively. The recombination rate constant can be obtained from the effective first-order relaxation time, A derivation analogous to (equation (B2.5.9). equation (B2.5.10). equation (B2.5.11) and equation (B2.5.12)) yield... 

Figure 2.11. Proton-Proton shift correlations of a-pinene (1) [purity 99 %, CDCls, 5 % v/v, 25 °C, 500 MHz, 8 scans, 256 experiments], (a) HH COSY (b) HH TOCSY (c) selective one-dimensional HH TOCSY, soft pulse irradiation at Sh = 5.20 (signal not shown), compared with the NMR spectrum on top deviations of chemical shifts from those in other experiments (Fig. 2.14, 2.16) arise from solvent effects...

In the laser flash method, a melt of interest is placed between two parallel plates. The upper plate is heated stepwise and the thermal diffusiv-ity is measured from the rise in temperature. The specific design for molten materials and especially slags employed by Ohta et al. is based on the differential three-layer technique utihzing a special cell that can be accommodated in the system. A schematic diagram of the principle of the measurement section is shown in Fig. 31. A laser pulse irradiates the upper (platinum) crucible and the temperature response of the surface of the lower platinum crucible is observed, a liquid specimen being sandwiched between the two. 

Figure 5.11 shotvs the temporal profile of the intensity change in the SFG signal at the peak of the Vco mode (2055 cm ) at OmV induced by visible pump pulse irradiation. The solid line is the least-squares fit using a convolution of a Gaussian function for the laser profile (FWFJ M = 20 ps) and a single exponential function for the recovery profile. The SFG signal fell to a minimum within about 100 ps and recovered... 

Figure 5.13 Transient CO migration induced by intense pump pulse irradiation.

Final resolution of these problems, particularly the complications from multiple matrix sites, came from investigations using spectroscopic methods with higher time resolution, viz. laser flash photolysis. Short laser pulse irradiation of diazofluorene (36) in cold organic glasses produced the corresponding fluorenylidene (37), which could be detected by UV/VIS spectroscopy. Now, in contrast to the results from EPR spectroscopy, single exponential decays of the carbene could be observed in matrices... 

Pre-saturation In this technique prior to data acquisition, a highly selective low-power rf pulse irradiates the solvent signals for 0.5 to 2 s to saturate them. No irradiation should occur during the data acquisition. This method relies on the phenomenon that nuclei which have equal populations in the ground and excited states are unable to relax and do not contribute to the FID after pulse irradiation. This is an effective pulse sequence of NOESY-type pre-saturation that consists of three 900 pulses RD - 900 - tx - 900 - tm - 90° - FID, where RD is the relaxation delay and t and tm are the presaturation times. 

The principles behind MAP liquid-phase and gas-phase extractions are fundamentally similar and rely on the use of microwaves to selectively apply energy to a matrix rather than to the environment surrounding it. MAP gas-phase extractions (MAP-HS) give better sensitivity than the conventional static headspace extraction method. MAP-HS may also be applied in dynamic applications. This allows the application of a prolonged, low-power irradiation, or of a multi-pulse irradiation of the sample, thus providing a means to extract all of the volatile analytes from the matrix [477]. 

Reaction of hexafluorobenzene and silane under single pulse irradiation of a MW CO2 laser was explosive. 

The mobility of eh was determined by measuring the equivalent conductance following pulse irradiation (Schmidt and Buck, 1966 Schmidt and Anbar, 1969). After correcting for the contribution of H30 and OH ions, they found the equivalent conductance of eh = 190 10 mho cm2. From this, these authors obtained the mobility p(eh) = 1.98 x 10"3 cm2/v.s. and the diffusion coefficient D(eh) = 4.9 x 10-5 cm2/s using the Nernst-Einstein relation, with about 5% uncertainty. The equivalent conductance of eh is the same as that for the OH - ion within experimental uncertainty. It is greater than that of the halide ion and smaller than that of eam... 

The hydrated electron reacts with H202 with a diffusion-controlled rate (see Table 6.6), giving OH and OH-. An intermediate product of this reaction, H202, may be responsible for prolonged conductivity in pulse-irradiated water. The rate of this reaction is consistent with rates of similar one-electron reduction reactions of H202. 

Rzad et al.( 1970) compared the consequences of the lifetime distribution obtained by ILT method (Eq. 7.27) with the experiment of Thomas et al. (1968) for the decay of biphenylide ion (10-800 ns) after a 10-ns pulse-irradiation of 0.1 M biphenyl solution of cyclohexane. It was necessary to correct for the finite pulse width also, a factor rwas introduced to account for the increase of lifetime on converting the electron to a negative ion. Taking r = 17 and Gfi = 0.12 in consistence with free-ion yield measurement, they obtained rather good agreement between calculated and experimental results. The agreement actually depends on A /r, rather than separately on A or r. 

Shimamori and Hatano (1976) describe a Febetron-injected microwave cavity apparatus for measuring electron concentration following pulse irradiation. Its application to thermalization in Ar and CH4 is similar to the method of Warman and Sauer (1975). In a related experiment, Hatano et al. (private communication) measure the electron collision frequency directly. 

Tembe and Mozumder (1984) applied the DPM method to calculate the time-dependent electron mobility in pulse-irradiated gaseous Ar. They used the gas kinetic formula for mobility (Huxley and Crompton, 1974),... 

Other microwave-assisted parallel processes, for example those involving solid-phase organic synthesis, are discussed in Section 7.1. In the majority of the cases described so far, domestic multimode microwave ovens were used as heating devices, without utilizing specialized reactor equipment. Since reactions in household multimode ovens are notoriously difficult to reproduce due to the lack of temperature and pressure control, pulsed irradiation, uneven electromagnetic field distribution, and the unpredictable formation of hotspots (Section 3.2), in most contemporary published methods dedicated commercially available multimode reactor systems for parallel processing are used. These multivessel rotor systems are described in detail in Section 3.4. 

Pulse radiolysis is used also for preparation of excited states of dienes and polyenes. This is done by irradiation of the diene/polyene in toluene solution. The radiolysis of toluene yield high concentration of molecules in the triplet excited state of the solute. Wilbrandt and coworkers61 pulse-radiolysed 1 mM solution of al I -lrans-1,3,5-heptatriene in toluene solution and observed the absorption spectra of the triplet state of the heptatriene with a maximum at 315 nm. The same group62 produced and measured the absorption spectra of several isomeric retinals in their lowest excited triplet state by pulse irradiation of their dilute solution in Ar-saturated benzene containing 10 2 M naphthalene. Nakabayashi and coworkers63 prepared the lowest triplet states of 1,3-cyclohexadiene,... 

Low temperature epr spectroscopy shows, not unexpectedly, that DCFL has a triplet ground state (Table 3). Pulsed irradiation of the diazo-compound in acetonitrile reveals transient spectra assignable to the triplet carbene, the radical (DCFLH ) and the ylid that are nearly identical with those recorded from irradiation of DAF under similar conditions (Rak et al., 1986). 

Figure 3. Time-resolved resonance Raman spectrum of the phenoxyl radical observed 1 ls after pulse irradiation of a 2 mM phenolate solution (N20 saturated) at pH 11 (excitation at399nm). [Adapted from (18b).]...

Measurement of time-resolved Ro(t) or R (0 under femtosecond-pulse irradiation. Evaluation with Monte Carlo simulation, /Vmethod, or numerical KM approximation. 

Fe (CN)jX species, pulse-irradiated at 530 nm, display bleaching within the 20 ns pulse. After bleaching, the original absorbance is redeveloped at rates linearly depending on the concentration of free X in solution. For 1 (but not 2) a second small absorbance change ( = 10%) accompanied the first. Explain this behavior. 

Laser photolysis offers new possibilities, allowing the study of much ftister processes. Once again the system 3,5-dinitroanisole and hydroxide ion was irradiated. The constructed absorption spectra (Figure 12) at different time intervals after pulse irradiation indicate two decaying absorptions with different lifetimes, probably representing two different species ... 

Affer drying fhe film completely in a vacuum for several days, a photocurrent was observed using the same electrode setup shown in Fig. 15, with pulsed irradiation of light above 380 nm using a 150 W xenon lamp (Hamamatsu Photonics). As shown in Fig. 15, a large ohmic phofocurrenf was observed when DNA strands were aligned perpendicular, but not paral-... 

Gelinck GH, Warman JM (1996) Charge carrier dynamics in pulse-irradiated polyphenyle-nevinylenes effects of broken conjugation, temperature, and accumulated dose. J Phys Chem 100 20035... 

Electrons have not been detected by optical absorption in alkanes in which the mobility is greater than 10 cm /Vs. For example, Gillis et al. [82] report seeing no infrared absorption in pulse-irradiated liquid methane at 93 K. This is not surprising since the electron mobility in methane is 500 cm /Vs [81] and trapping does not occur. Geminately recombining electrons have, however, been detected by IR absorption in 2,2,4-trimethyl-pentane in a subpicosecond laser pulse experiment [83]. The drift mobility in this alkane is 6.5 cm /Vs, and the quasi-free mobility, as measured by the Hall mobility, is 22 cm /Vs (see Sec. 6). Thus the electron is trapped two-thirds of the time. 

Bakale et al. [397] pulse irradiated the hydrocarbons cyclopentane, cyclohexane and n-hexane with 0.9 MeV electrons of duration 10 or 100 ns. The transient conductivity decreased approximately exponentially with time for low doses of radiation. The first-order decay of the conductance is probably due to electrons reacting with impurities. With higher doses, the conductance decays approximately as inverse time, characteristic of a second-order recombination of free ions. No evidence for time-dependent geminate ion-pair recombination effects was observed. 

The above-mentioned experiments on the femtosecond MPI of molecules on a surface have shown that under femtosecond pulse irradiation conditions the formation threshold of molecular ions is reduced by a factor of around 10 compared to that in the case of irradiation with femtosecond pulses. This is evidence that the MPI of the chromophores under the effect of femtosecond pulses occurs directly on the tip surface and prior to their desorption (Fig. 2). 

A 180" pulse irradiating the protons just inverts the rotation of the doublet vectors (Fig. 2.38(b)). At time 2t, the components refocus along the positive y -axis (Fig. 2.38(b)), so that a positive signal arises from Fourier transformation. 

As with gamma radiation. X-rays in the steady-state mode have not produced any initiations in any of the expls irradiated. Effects are being directed towards intense, pulsed irradiations in order to simulate nuclear weapons effects. The prospect of higher dose rates in short time frames should produce results not common, to the steady-state irradiation... 

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