Short-lived transient species solutions

The use of pulse radiolysis and scavenging techniques has identified the electron in liquid hydrocarbons [116]. In these non-polar media, interaction between the electron and the solvent is, of course, very small and it is doubtful whether such electrons can properly be described as solvated. The pulse radiolysis of hexane or 3-methyl hexane gave rise to a short lived transient species absorbing at Xm ax = 1500 nm. Rate coefficients for reaction in hydrocarbon solutions at 193°K are given in Table 10. Baxendale et al. [117] have studied the pulse radiolysis of liquid methylcyclohexane and obtained rate coefficients for the reactions of the electron with carbon tetrachloride and pyrene at 293° K. Relative rate coefficients have been obtained by irradiation of hydrocarbons containing two electron scavengers [118]. 

Photolysis of Short-Lived Transient Species in Solutions Product Analysis Studies... 

The Fenton-type chemistry between Fe q and several rhodium hydro-peroxides yields Rh(IV) species believed to have the general formula L(H20)Rh0, Eq. (11) (72 although this was not established experimentally for these short-lived transients. Just like the other LMO species generated by this route (58 the compounds L(H20) RhO (L = (NH3)4, L, and L ) react rapidly with the Fe + present in solution. The addition of substrates for L(H20)Rh0 resulted in a competition, as shown for methanol in Eqs. (12) and (13). 

Silylenes are short-lived intermediates, and their detection requires fast methods such as ultraviolet (UV)24 or laser-induced fluorescence spectroscopy.25 The characteristic absorption maxima in the UV-visible spectra of these species, which are assigned to n - p transitions of electrons at the silicon atom, were used as a fingerprint to prove the occurrence of silylenes in matrices or solution. In addition, these transient species, which under normal conditions are too short lived to be observed by a slow detection method such as infrared (IR) spectroscopy, can be isolated in inert hydrocarbon or noble gas matrices, thus allowing the accurate measurement of their IR spectra. 

The transient absorption spectrum obtained from the pulse radiolysis of CMS solutions in benzene as shown in Fig. 2 (b) is very similar to the absorption spectrum obtained in a solid resist film as shown in Fig. 2 (a). However, the absorption in solution around 500 nm is mainly due to the complex of benzene with chlorine atoms whereas in the solid film, it is due to the complex of the phenyl ring of CMS with Cl. The absorption due to Pj is observed in both solid CMS film and CMS solutions in benzene. The absorption around 320 nm may be due to the biradical of benzene. The very short lived species with absorption around 500 nm is mainly due to the benzene excimer with a small contribution from the CMS excimer. Benzene solutions of CMS have proven to be a very good model system for reactions occurring in solid films of CMS. 

The direct characterization of an eT mechanism requires a much more complicated technique time-resolved spectroscopy. The solution containing the system under investigation is irradiated by a laser pulse, and the absorption spectra of the solution are consecutively recorded at chosen and very short time intervals (e.g. every 10 ns). If, in the envisaged two-component system F1 M, an M-to-Fl eT process takes place upon illumination, one should be able to measure the absorption spectra of Fl and M" ", as well as their decay, which allows the determination of the lifetime of the transient species F1 M. It goes without saying that very sophisticated and expensive instrumentation is required to carry out this type of experiment. Moreover, the smaller the fluorophore lifetime and the faster the back-electron transfer process, the more rapid and expensive the data acquisition equipment required. In particular, narrow laser pulses and especially fast data collections are needed for systems such as 1, where a short-living polyaromatic fluorophore (anthracene, r = 5 ns) is linked to the electron donor (or acceptor) group by a rather short carbon chain. 

Although EPR signals related to hydrocarbon cations radicals generated by electrochemical oxidation or chemical oxidation can be readily detected, only a few examples have been reported for cation radicals that are produced by irradiation of solutions of electron donors and an acceptor. Because electron spin polarization offers the advantage of detecting transient species via their EPR signal intensities, chemically induced dynamic electron polarization (CIDEP) spectra can give information not only about short-lived radical intermediates... 

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