Triplets short-lived transient species

Using these characteristics of lasers, photochemical reactions that cannot be conducted with conventional Hght sources can be brought about, and a multiphoton reaction is one of these processes. Multiphoton reactions can be classified in two categories (1) stepwise reactions through short-lived transient species (Path 1 in Scheme 1) and (2) reactions by concerted multiphoton absorptions (Path 2 in Scheme 1). In many cases. Path 1 predominates when the substrates are complex organic compounds. The transient species can be either long-lived excited states, such as triplet states, or chemical species, such as radicals, carbenes, nitrenes, and thermally unstable molecules. 

The photooxidation of CS2 and COS has also been examined in flash photolysis studies. The spectra of a number of sulfur oxides have been detected. Both SO2 and SO have been definitely identified A system of absorption bands appearing between 2500 and 2400 A. have been assigned to the sulfur monoxide molecule, S2O, on the basis of mass spectrometric evidence. A transient spectrum observed in the wavelength region, 1840-1740 A., has been tentatively assigned to a short-lived isomeric form of sulfur dioxide, the structure of which may be SOO, sulfur superoxide. The probable precursor of all these species is the sulfur monoxide which arises from the reaction of atomic sulfur with O2. The overall reaction is complex a number of possible steps have been postulated to account for the intermediates, SO and SOO, as well as for the final products S2O and SO2. With triplet sulfur atom, the most likely reaction to produce SO is S( P) -H Ojf S,-) S0(32 ) -I- 0(V) (43)... 

Spectra.—Ultraviolet Spectra, The transient, extra absorption band which appeared in the 400—600 nm region (maximum absorption at ca. 475 nm) in the u.v. spectrum of thiobenzophenone as a result of the flash photolysis of this thione has been tentatively assigned to short-lived, triplet thio-benzophenone. " A similar species, generated in the same manner from Michler s thione, was found to exhibit absorption in the 470—520 nm region. " The influence of substituents (R) on the u.v. absorptions of 3-alkyl- and 3-aryl-6-methylthiouracils (368) has been studied, and, based on a comparison with the u.v. spectra of alkyl-, aryl-, and benzoyl-thioureas, the two bands at 280 nm and 240 nm (the intensities of which... 

Although relatively short-lived, radical cations are the primary products of the electron transfer (ET) step. Evidence for the formation of radical cations has been presented for silyl enol ether systems that form stabilized radical cations. Kochi and coworkers investigated the photoinduced electron transfer between different silyl enol ethers and chloranil in detail.In a system suitable for the spectroscopic study of the radical cation intermediate, chloranil (CA) is electronically excited to its triplet state CA (10). Subsequent electron transfer generates the corresponding radical ion pair (11/12). All these transient species have been observed by time-resolved spectroscopy. 

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