Ultraviolet induced photolysis

No information was found on the transformation of diisopropyl methylphosphonate in the atmosphere. Based on the results of environmental fate studies of diisopropyl methylphosphonate in distilled water and natural water, photolysis (either direct or indirect) is not important in the transformation of diisopropyl methylphosphonate in aquatic systems (Spanggord et al. 1979). The ultraviolet and infrared laser-induced photodegradation of diisopropyl methylphosphonate in both the vapor or liquid phase has been demonstrated (Radziemski 1981). Light hydrocarbon gases were the principal decomposition products. Hydrogen, carbon monoxide (CO), carbon dioxide (C02), and water were also detected. 

Photolysis Reactors and Ultraviolet Sources. For 253.7-m/ irradiation, a modified irradiation apparatus purchased from Delmar Co. was used. The reactor was a 2-necked, 500-ml., round-bottomed flask. One neck was an O-ring joint, and the other was a 24/40 joint. A 4- X 1-inch coiled low pressure mercury quartz lamp was placed inside the flask through the O-ring neck, and the joint was sealed with removable O-rings. The reactor was connected directly to the mass spectrometer by the 24/40 joint. The samples were placed inside the flask and irradiated internally. The O-ring was shielded from direct radiation so as not to induce degradation. The estimated output of the lamp was 30 watts, and the ambient temperature within the reactor during irradiation was 70°C. 

Ashfold and Simons (47a) have recently shown that both CN(/l2ri) and (B E+) states are formed in the vacuum ultraviolet photolysis of BrCN. At the low pressure limit CN(B3 + ) shows a vibrational population inversion at the 1236 A photolysis (a maximum at o = 2), while at higher pressures the population shows a monotonic decrease with an increase of o observed before by Mole and Okabe (692). They attribute the pressure elTect to the collisionally induced inicrsystcm crossing between the /t2Il (o > 10) and neighboring B2Z + (o > 0) levels. Because of the long radiative life of A2n sialc ( - 7 /isec) (532), it is susceptible to collisions even at a pressure of 10 mtorr. 

Noxon calculated the rate constant of O( D) quenching by 02 on the basis of unit quantum yield and of the equilibrium concentration of 0( >) atoms. His value of 6 x 10 11 cm3 molec"1 sec-1 agrees well with 7 x 10"11 cm3 molec"1 sec" 1 obtained independently (456), indicating that the assumption of unit quantum yield may be justified. Below 1332 A the production of O( S) is energetically possible. Filseth and Welge (348) have observed an emission at 5577 A due to the transition O( S)- O( D) in the flash photolysis of 02 below 1340 A. The intensity is so weak that Xe has to be added to induce the transition. No quantum yield of O(. S) production has been measured. Recently Stone et al. (937) have measured the llight time ofO atoms produced in the Hash photolysis of the molecular beam of 02 in the vacuum ultraviolet. The O atoms are detected by the chcmiionization reaction with samarium. The technique is similar to the one described in Section II 4.1. 

Bamford et al. (45) have recently studied the photolysis of H2CO near the S- origin. The complete rotational distribution has been obtained for CO, which was detected by vacuum ultraviolet laser induced fluorescence. The distribution has a peak at J" = 42 and highly nonthermal, suggesting that energy randomization does not occur during dissociation. The population in CO J" < 20 is absent. The vibrational population of v" = 1 is 14 5% as large as that of CO (v" = 0). The C0(v" = 1) has nearly the same rotational distribution as C0(v" = 0). 

Experimental Techniques A absorption CIMS = chemical ionization mass spectroscopy CK = competitive kinetics DF discharge flow EPR = electron paramagnetic resonance FP = flash photolysis FT = flow tube FTIR Fourier transform intra-red GC = gas chromatography, UF = laser induced fluorescence LMR = laser magnetic resonance MS = mass spectroscopy PLP = pulsed laser photolysis SC = smog chamber SP = steady (continuous) photolysis UVF = ultraviolet flourescence spectroscopy... 

The photolytic excitation of charge-transfer complexes is another recent addition to the available physical expedients to promote cationic polymerisation. The cation radicals generated by the photolysis have been characterised in some systems. More recent still is the use of ultraviolet radiation to induce the photolysis of substances whose photoproducts are initiators of cationic polymerisation. These processes will be discussed in Chap. Vin. 

Oxygen saturated polyethylene glycol (283) shows an absorption band in the ultraviolet which is ascribed to a CT-absorption. Photolysis induces the formation of peroxidlc compounds. Glycol-aldehyde is an Important end product. 

Photolysis. Chemical reaction (synthesis or degradation) induced by absorption of ultraviolet or visible radiation. 

A final point about radiation-induced reactions with covalent bonds at the surface is that a purely electronic event, the ionization of a bond in a surface group or molecule, may lead to an atomic displacement. If a bond is broken by the ionization, the thermal motion of the fragments involved can result in their diffusion to new locations without the necessity for appreciable momentum interchange with the causative radiation. Thus even photolysis of surface molecules might lead to atomic displacements, an eventuality not possible in straightforward radiation damage with such low-momentum radiation as ultraviolet. 

Rate constants for reaction of the CH radical with a number of atomic and molecular collision partners have been reported, with multiple-photon dissociation of suitable precursor molecules using either infrared or ultraviolet " laser radiation used as the pulsed photolysis source, and laser-induced fluorescence near 431 nm employed as a sensitive time-resolved detection method. A similar technique has been used to measure removal rates of CH2 and CDj with... 

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