Spectroscopy transient absorption difference

The photoinduced electron transfer reactions have also been studied with nanosecond transient absorption spectroscopy [67]. The transient absorption difference spectrum for the reaction of 12a and 4-(methoxycarbonyl)-A/-methylpyr-idinium is shown in Fig. 4. The difference spectrum is characterized by a sharp intense absorption at approximately 390 nm, a Iowa- intensity band at 484 nm, and an intense broad absorption band at approximately 693 nm. The sharp band at around 390 nm is characteristic of pyridinyl radical absorption. The reaction mechanism is depicted in Scheme 1. 

The photoinduced electron transfer behavior has also been confirmed by nanosecond transient absorption spectroscopy [102,103,108,111]. A representative transient absorption difference spectrum recorded 10 ps after laser flash excitation of 24a (0.05 mM) and 4-(methoxycarbonyl)-A[-methylpyridinium hexaflu-orophosphate (13 mM) in degassed acetonitrile (0.1 M "Bu4NPF6) is shown in... 

Structure, then the time-resolved photoelectron spectra [20, 21] could reveal signatures of two different intermediate structures, representing two different pathways on the PES. Transient absorption spectroscopy and other femtosecond time-resolved techniques may also be applicable to this problem. 

The dynamics of photoinduced charge separation, kcs, and charge recombination, kcr (Fig. 2a), have been studied in several families of hairpins containing an Sa linker and a single G C base pair by means of femtosecond time-resolved transient absorption spectroscopy [27, 28]. Both the singlet state and anion radical of Sa have strong transient absorption centered at 575 nm. The difference in the independently determined band shapes for Sa ... 

In flash spectroscopy a second spectroscopic flash is fired a short time after the photolysis flash and the transient absorption spectrum is registered on a photographic plate (Fig. 13). Repeating the experiments with different delay times gives complete information about the wavelength and the time behavior of the intermediate absorptions. 

The nickel proteins and the native iron globins show the same behavior in regard to fifth-ligand photodissociation but for totally different reasons. Heme proteins and other metal-reconstituted heme proteins have been investigated by transient absorption spectroscopy (49-53) and transient Raman spectroscopy (16,54-62). In none of the Fe proteins is loss of the histidine ligand observed even on a picosecond timescale. Soret excitation of carbonmonoxy and oxy Hb and Mb photolyzes CO or O2, but not the histidine fifth ligand. 

Fig. 3. Pump-deplete-probe spectroscopy on lycopene in hexane, a) Experimental setup After excitation and depletion of Car S2 with a delay of r=50fs, a white-light probe pulse at delay tprob<.=2ps measures the transient absorption spectrum, b) Spectra without (solid curve) and with depletion pulse (dotted) and their difference (shaded area). Only the Car Si state is depleted the ground state bleach (S0-S2) and positive absorption feature on its low energy side (hotSo-S2) are unaffected.

Ethylene glycol is a very viscous liquid and the molecule presents two close OH groups. It has to be noticed that, among all the different solvents studied by pulse radiolysis, the transition energy of the solvated electron absorption band is maximum in liquid ethylene glycol. For these reasons, the electron in EG seems to have a special behaviour and it is of great interest to study the dynamics of the formation of equilibrated solvated electron. Within this context, the present communication deals with the dynamics of solvation in EG of electrons produced by photoionisation of the solvent at 263 nm. The formation of solvated electrons is followed by pump-probe transient absorption spectroscopy in the visible spectral range from 425 to 725 nm and also in near IR. For the first time, the absorption spectrum of the precursor of the equilibrated electron is observed in EG. Our results are shortly compared by those obtained in water and methanol. 

Most recently the TICT model has been verified by transient absorption spectroscopy,234 that is, by time-resolved studies of vertical transitions which start from different points on the horizontal reaction pathway. 

These conclusions were supported by transient absorption spectroscopy, which revealed signals corresponding to the formation of the diimine radical anion, with lifetimes in close agreement with the luminescence lifetimes. Time-resolved infrared spectroscopy of the acetylide C = C bonds provides further conclusive evidence for the MLCT assignment. Thus, in the ground state IR spectrum of 4, there are two v(C=C) bands at 2115 and 2124 cm-1, whilst the step-scan FTIR difference spectrum obtained 50 ns after irradiation at 355 nm reveals bleaching of the parent bands, and the formation... 

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