Excimer lamps production

The vacuum-UV photolysis of water (Fig. 5-9, reaction 9) with incoherent xenon excimer lamps (X=172nm) (cf Chapter 7.1.3) or with low-pressure Hg lamps (Suprasil envelope, X= 184.9 nm) is an example of a process used for hydroxyl radical production (and of other reactive species) without the addition of any auxiliary oxidant... 

Tab. 7.4 Examples of research related to homogeneous and heterogeneous photo-initiated AOPs in the gas phase. Examples of applications of incoherent excimer lamps are collected in Table 7-2. Ox intermediary oxidation products formed and detected during treatment... 

However, the photochemical production of ozone on a small scale represents a potential application of the novel incoherent Xe2 excimer lamps. This was first demonstrated by Eliasson and Kogelschatz (1991), and on laboratory and preparative scales by Laszlo et al. (1998) and by Hashem et al. (1997). The latter research group realized the simultaneous generation of ozone in the gas phase and its transfer to the aqueous phase followed by the VUV irradiation of this water by... 

Excimer lamps were selected to study the low fluence irradiation region, where linear (no ablation) photochemistry is taking place. This is the fluence range (e.g., insert in Fig. 47 of the previous chapter), where a linear relation between reaction products and laser fluence is observed. This may correspond to the range of linear photochemistry, i.e., below the threshold of ablation (see, e.g., Figs. 25 and 26), or the so-called Arrhenius tail. The excimer lamps emit at the same wavelengths as the excimer lasers, but with incoherent radiation, and in quasi-CW mode. The peak photon fluxes of the lamps are low compared to the excimer laser, suggesting that multiphoton processes are not important. Thin films of the triazene polymer on quartz substrates were irradiated with the excimer lamps under different conditions, i.e., in Ar, air, and 02. 

In addition to the rather trivial differences mentioned above, laser irradiation can also lead to products as a result of reexcitaion of the carbenes. Thus, excitation of 30 in isooctane with a pulse of the 249-nm line from a KrF excimer laser results in the formation of 9,10-diphenylanthrancene (103), 9,10-diphenylphenanthrene (104), and fluorene, in addition to tetraphenylethylene (Scheme 9.31). Conventional lamp irradiation of 30 results in the formation of benzophenone azine as a major product. None of the products mentioned above are detected. Moreover, the yield of both 103 and fluorene increased markedly with increased laser power. While the details of the mechanism of this reaction are not certain yet, it is clear from the dependence on laser power that some of these products arise from carbene photochemistry. " ... 

Irradiations of alkenes are generally conducted with a low-pressure mercury lamp (185 nm), an ArF excimer laser (193 nm), or a zinc resonance lamp (214 nm). Highly substituted alkenes can also be irradiated with a medium-pressure lamp and quartz optics (>200 nm). Because of the presence of two or more close-lying singlet excited states, irradiation of alkenes usually results in several competing photoprocesses. Thus, for example, irradiation of 2,3-dimethyl-2-butene (1) in hydrocarbon or ether solvent results in rearrangement to the carbene-derived products 4 and 5 and the double bond isomer 9. E,Z-Isomerization also occurs but is not apparent in this case because of the symmetry of alkene 1. Similar behavior is exhibited in the gas phase. In alcoholic or aqueous media, the nucleophilic trapping products 8 are formed in competition with the carbene-derived products 4 and 5. ... 

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