Irradiation vapour pressure

In 1983 Suslick reported the effects of high intensity (ca. 100 W cm, 20 kHz) irradiation of alkanes at 25 °C under argon [47]. These conditions are of course, well beyond those which would be produced in a reaction vessel immersed in an ultrasonic bath and indeed those normally used for sonochemistry with a probe. Under these extreme conditions the primary products were H2, CH4, C2H2 and shorter chain alk-l-enes. These results are not dissimilar from those produced by high temperature (> 1200 °C) alkane pyrolyses. The principal degradation process under ultrasonic irradiation was considered to be C-C bond fission with the production of radicals. By monitoring the decomposition of Fe(CO)5 in different alkanes it was possible to demonstrate the inverse relationship between sonochemical effect (i. e. the energy of cavitational collapse) and solvent vapour pressure [48],... 

Krause et a/.123-125 have recently reported a series of measurements of the spin-orbit relaxation of the alkali metals in their first excited states (2P). The technique, for example for atomic caesium with AE = 554 cm-1, consists of irradiating the metal vapour with light from a monochromator to excite only one of the 2P states. The vapour pressure of the metal is controlled at 10-6 torr to avoid imprisonment of the resonance radiation. The components of the fluorescence light are measured with a photomultiplier by isolating the 2P - 2S lines with interference filters. In the presence of added gases which cause the transitions... 

Moore [355] used the solvent extraction procedure of Danielson et al. [119] to determine iron in frozen seawater. To a 200 ml aliquot of sample was added lml of a solution containing sodium diethyldithiocarbamate (1% w/v) and ammonium pyrrolidine dithiocarbamate (1 % w/v) at pH to 4. The solution was extracted three times with 5 ml volumes of 1,1,2 trichloro-1,2,2 trifluoroethane, and the organic phase evaporated to dryness in a silica vial and treated with 0.1 ml Ultrex hydrogen peroxide (30%) to initiate the decomposition of organic matter present. After an hour or more, 0.5 ml 0.1 M hydrochloric acid was added and the solution irradiated with a 1000 W Hanovia medium pressure mercury vapour discharge tube at a distance of 4 cm for 18 minutes. The iron in the concentrate was then compared with standards in 0.1 M hydrochloric acid using a Perkin-Elmer Model 403 Spectrophotometer fitted with a Perkin-Elmer graphite furnace (HGA 2200). 

The explosive phenomena produced by contact of liquefied gases with water were studied. Chlorodifluoromethane produced explosions when the liquid-water temperature differential exceeded 92°C, and propene did so at differentials of 96-109°C. Liquid propane did, but ethylene did not, produce explosions under the conditions studied [1], The previous literature on superheated vapour explosions has been critically reviewed, and new experimental work shows the phenomenon to be more widespread than had been thought previously. The explosions may be quite violent, and mixtures of liquefied gases may produce overpressures above 7 bar [2], Alternative explanations involve detonation driven by phase changes [3,4] and do not involve chemical reactions. Explosive phase transitions from superheated liquid to vapour have also been induced in chlorodifluoromethane by 1.0 J pulsed ruby laser irradiation. Metastable superheated states (of 25°C) achieved lasted some 50 ms, the expected detonation pressure being 4-5 bar [5], See LIQUEFIED NATURAL GAS, SUPERHEATED LIQUIDS, VAPOUR EXPLOSIONS... 

Lewis and Mayer f made experiments to test whether the decomposition in the gas phase is accelerated by irradiation with the appropriate infra-red radiation. The pinene vapour was caused to stream at low pressure through a vessel intensely irradiated with infra-red radiation. The result was that none of the racemization which would have been expected on the basis of the radiation theory took place. 

In the real polydisperse foam along with coalescence there always acts another process of internal collapse. This is the diffusion decrease in the specific surface which is accompanied by structural rearrangement, i.e. shift of knots and borders, and change in their orientation. This leads to the origination of various local disturbances (Act, Apa, AC, etc.). These local disturbances along with the rupture of individual films cause destruction either of other films and borders or of local volumes or of the whole foam (see Sections 6.5 and 6.6). Finally, various external factors can affect the foam (pressure drop, applied to the liquid phase reduced pressure of the liquid vapour above the foam, leading to evaporation the effect of antifoam droplets a-particle irradiation vibration, etc.). 

The physical means of defoaming involve foam breakdown by thermal treatment (heating, processing with overheated vapour, freezing), by acoustic (mainly ultrasound) waves, vibrations, a-particles irradiation, creation of high capillary pressure in the foam, etc. 

The CO2 laser-induced multiphoton decomposition of silanes, known to be a really homogeneous reaction, was utilized for the chemical vapour deposition of fluorine containing SiC films from the parent (fluoromethyl)silanes [25, 26]. In contrast to work with H3CS1H3, irradiation of (fluoromethyl)silanes with a single unfocused CO2 laser pulse at fluence of S 0.9 Jcm" tuned to absorption bands of either the SiH bending or the CF stretching vibrations results in an explosive reaction. This is accompanied by an intense chemoluminescence when the sample pressure exceeds a certain limit in the range of 0.1-6.7 kPa (Fig. 1). 

The irradiation light source is a Hanovia 450 W medium-pressure Hg vapour lamp placed in a quartz immersion well. The reaction solution is contained in a 150 ml quartz semicircular flask mounted as closely as possible to the immersion well. No light filter is used. The entire apparatus is immersed in a large Dewar flask charged with dry ice-isopropanol with the bath temperature maintained between —60 and —40°C during irradiation. 

Metal atom clusters in the 26-hedra could (as with water molecules) contain many metal atoms. An example is the fourteen atom Agg+8Ag+ cluster in Y-irradiated zeolite Ag-A[25]. Saturation is achieved for mercury sorbed into silver-exchanged faujasites and other zeolites [26]. The Ag+ is reduced to Ag atoms and then at an approximate critical pressure of mercury vapour there is nucleation of mercury clusters which fill all the pore volume as the pressure of Hg vapour increases further. Mercury-zeolite systems are the oily ones in which sorption isotherms have been investigated quantitatively. Hcwever other metal atoms introduced into zeolites (by ion exchange and reduction, or as metal carbonyls and their decomposition) all show, on heating, a strong tendency to form clusters by migration of atoms, which can aggregate both within and outside the crystals. 

A soln. of startg. pyranocarbazole in benzene irradiated at room temp, in a quartz immersion well photochemical reactor using a low- or medium-pressure Hg-vapour lamp (400 W 365 nm) under Nj for 4 h - product. Y 60%. F.e.s. A. Chakrabarti, D.P. Chakraborty, Tetrahedron Letters 29, 6625-8 (1988). 

---