Acid glasses, irradiation

Ultraviolet irradiation of O, O -dialkyldithiophosphoric acid glasses at liquid nitrogen temperatures leads to the formation s ) of radical species of the type... 

Fig. 11. New absorption spectrum (solid line) appearing reversibly on irradiation of fluorescein in boric acid glass. The dotted line shows the normal absorption spectrum. After G. N. Lewis et al., J. Am. Ckem. Soc., to, 3005 (1941).

This interpretation indicates that the oxidizing radical is thermodynamically favored over the reducing radical. This is confirmed by quantum mechanical calculations (Naumov and von Sonntag, unpubl. results Wu et al. 2004), and when low-temperature sulfuric acid glasses containing Ura or Thy are X-irradi-ated, the dominant radical seen by EPR is the 5-yl radical (Riederer and Hut-termann 1982). 

Confirmation that the emitting species in phosphorescent organic molecules is a triplet has come from several sources. In the 1940s it was discovered that a solution of fluorescein in boric acid glass became paramagnetic under intense irradiation more recently it has been shown that the paramagnetism and the phosphorescence decay at identical rates when irradiation ceases. The electron paramagnetic resonance (EPR) technique is capable of detect-... 

Optical absorption to a higher triplet has afforded further evidence that the emitting state in phosphorescence is a triplet. Intense irradiation of a boric acid glass containing fluorescein leads to the appearance of a new absorption band due to triplet-triplet absorption. Flash photolysis, in which a sample is exposed to a brief, intense flash of light, can be used to produce high transient concentrations of triplet species kinetic absorption spectroscopy of the system enables the build-up and decay of several singlet and triplet levels to be followed as a function of time. 

In fact, the dominant radical seen by EPR when uracil is y-irradiated in low-temperature sulfuric-acid glasses, is the 5-yl one [34], which supports this contention under the assumption that the nucleobase is not protonated under these conditions. 

Nakano et al [160] prepared a copolymer of poly(vinyl acetate) and methacrylic acid by irradiation at 200 kHz. From measurements of viscoelasticity and from differential thermal analysis, it was concluded that the copolymer was of the block type. The glass transition temperature of this block copolymer was surprisingly reported to be much lower than those of random and graft copolymers. 

As metal ions catalyze peiroxidation reactions, glass-distilled water should be used and chelating agents can be added to the medium. (5) The dispersions should not be exposed to y irradiation. (6) Antioxidant can be added to the system. a-Tocopherol, buty-lated hydroxytoluene, butyl hydroxyanisole, and ascorbic acid have been proposed as antioxidants. 

Figure 10.7 The phase diagram (a) and the glass transition temperatures (b) of a PSC/PVME mixture obtained, respectively, by light scattering and differential scanning calorimetry (DSC). Irradiation experiments were performed in the miscible region at 127 C indicated by (X) in the figure of trans-cinnamic acid-labeled polystyrene/poly(vinyl methyl ether) blends.

The isocyanates were added to the respective resin-bound amines suspended in dichloromethane in open glass tubes. The resulting reaction mixtures were each irradiated in a single-mode microwave cavity for 2 min intervals (no temperature measurement given) (Scheme 7.52). After each step, samples were collected for on-bead FTIR analysis. Within 12 min (six irradiation cycles), each reaction had reached completion. Acid cleavage of the polymer-bound ureas furnished the corresponding hydrouracils. 

Cerium was included in a list of 14 elements determined by Lee et al. [627] in seawater using neutron activation analysis. The metals were first precon-centraed on a mixture of Chelex 100 and glass powder. The elements were desorbed from the column by 4 M nitric acid, and aqueous solution was irradiated for 3 days and subjected to y-ray spectrometry method with a Ge(Ii) detector coupled to a 4000-channel analyser. Cerium was found to be present to the extent of 16.7 xg/l in water taken from the Kwangyang Bay (South Korea). 

Irradiation. Samples of the polymers were weighed into small glass ampoules and evacuated at ca. 100 Pa for at least 48 h before sealing. During evacuation the samples of poly (amino acid)s and aromatic polysulfones were heated to assist in removal of occluded moisture. 

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