Photolysis Cell

Fig. 3. Schematic diagram of the Northwestern apparatus for IR laser kinetic measurements in the gas phase. D, and D2 are InSb detectors with D2 being a high speed photovoltaic detector. M = Mirror, I = iris, C = chopper, BS = beam splitter, P = photolysis cell. [Reproduced with permission from Ouderkirk et al. (75).]...

The equipment at the University of California (Davis) (59,76) is broadly similar to the Northwestern apparatus but photolysis cells up to 1 m long are used. A full description has been published recently (76). 

The glass photolysis cell has a radius of. 75 cm and an active length of 10 cm. The CaF2 windows of the cell are protected from photoproducts by a curtain of rare gas which flows over the windows and out the exhaust ports without mixing with the sample gases. 

Figure 1. Transient IR spectra following photolysis of Fe(C0>5 with XeF and KrF laser radiation. Traces are taken -1 nsec after photolysis. In addition to Fe(C0>5 (30 mtorr for KrF, 200 mtorr for XeF) the photolysis cell contained 5 torr Ar. The symbols are defined in the text.

The illumination source was a xenon illuminator (Cermax, ILC Technology, Sunnyvale, Cal.) operated at 180-320 W and situated 34-38 cm from the photolysis cell. The spectrum of the output of this lamp closely simulated the solar spectrum over the 300-700 nm wavelength region. To avoid thermal decomposition of samples undergoing illumination, the near-infrared component of the lamp output was attenuated by inserting a 20-cm water filter between the lamp and a sample. A portion of each sample of adsorbed PAH was stored in the dark, as a control, to ensure that no detectable non-photochemical decomposition of the PAH occurred during the duration of illumination. 

Figure 3 shows a schematic view of a flow reactor. It is similar to the photochemical reactor previously described in [5] but the UV photolysis cell has been replaced by a 1 m. stainless steel coil in a heated oil bath. As before, FTIR is used to monitor the conversion and optimise the conversion of reactant to product. Using such a system (C5Me5)Mn(CO)2(C2H4) can be obtained in a high yield as in Scheme 1. We are now scaling up this miniature reactor to a technical scale, ultimately with the aim of carrying out solvent-free reactions on a kilogramme scale.

An experimental setup similar to the Zimmerman photolysis cell was utilized by Lazare et al. (60) to determine the quantum yield for the photoreaction of a substrate adsorbed on silica gel. The photolysis cell consists of an aluminum dish for the powdered silica gel sample, which is covered by a double-walled hemispherical Pyrex cap filled with ferrioxalate actinometers solution. The sample is irradiated through a quartz light pipe, which enters the photolysis cell through a hole at the top of the cap. Thus, nearly all scattered light from the silica gel sample is absorbed by the surrounding actinometer solution, and the amount of light absorbed by the substrate (which is adsorbed on the silica gel surface) is determined by a similar subtraction method as described in the Zimmerman experiment (vide supra). 

The experiments were carried out in a conventional multiport flash photolysis cell. CH3 and H radicals were both generated from the flash... 

Wetmore and Taylor (47) investigated the methylamlne photolysis and found the decomposition rate of the Hg-photosensitized reaction equal to that of the direct one where a plug of gold wire was interposed between the vacuum system and the photolysis cell to exclude Hg. It seems possible though that Hg was present in both cases. Photolyses carried out with the light of low-pressure Hg arc lamps were, at least in part, Hg-sensltlzed if the contamination of the photolysis vessels by the Hg vapor present in the vacuum system was not rigorously excluded. This holds true especially for the early work. 

Mass spectra of short-lived, unstable episelenides were obtained by taking advantage of a mass spectrometric technique developed for the time-resolved detection of transient intermediates in flash-photolyzed systems <66JA4277>. Detection does not depend on the electronic absorption characteristics of the transient, and, in combination with kinetic absorption spectroscopy, the technique assumes great flexibility. The apparatus consists, essentially, of a photolysis cell attached to a small leak into the ion source of an Atlas CH4 mass spectrometer. Selected mass peaks can be studied with a response time of a few milliseconds, and thereafter at times limited by bleeding of the photolyzed mixture into the ion chamber. Typical photolytic flash energies were 480 calories, passed into a reaction volume of 5 ml. 

McFarland et al. (1979) 1974 Tropical Pacific Ocean noontime values 4 NO value CL, photolysis cell diurnal... 

Liu et al. (1983) Tropical Pacific Ocean, 2.8-5.7 NO CL, photolysis cell, diurnal... 

Figure 4.2-8 Layout of the semiflow reactor for the synthesis and isolation of Cp Mn(CO)2(tl -H2) from Cp Mn(CO)2 L ( L = labile ligand) and H2 in SCCO2. The reactor is very similar to that shown in Figure 4.2-7 but without the UV photolysis cell. Here the variable volume view-cell R is used as a thermal reactor. All other components are labeled as in Figures 4.2-6 and 4.2-7 (reproduced with permission from P. D. Lee, J. L. King, S. Seebald, M. Poliakoff, Organometallics 1998, 77, 524 American Chemical Society).

Compare the size of the 360-nm transient with photolysis cell surrounded by filter solutions with various wavelength cutoffs. 

Arakawa on-hne apparatus operates by directly irradiating a sample solution passing through a quartz photolysis cell located in the middle of the ESI spray tip to detect intermediates with lifetimes of more than few minutes (Figure 5.3). A light shutter equipped with a UV cutoff filter is mounted at the exit of the lamp to control photoirradiation. This set allows two different modes of irradiation. The first one, defined as cell mode irradiation, consists of the direct irradiation of the sample... 

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