Gas phase photochemistry

Hippier H and Troe J 1989 Advances in Gas Phase Photochemistry and Kinetics ed M N R Ashfold and J E Baggett (London Royal Society of Chemistry) pp 209-62... 

The record m the number of absorbed photons (about 500 photons of a CO2 laser) was reached with the CgQ molecule [77]. This case proved an exception in that the primary reaction was ionization. The IR multiphoton excitation is the starting pomt for a new gas-phase photochemistry, IR laser chemistry, which encompasses numerous chemical processes. 

One might conclude this first section by commenting that the combination of room-temperature and cryogenic techniques now available promises to unravel some photochemical problems of considerable complexity. Before turning to some further examples, it is worth noting some very interesting recent experiments involving the gas phase photochemistry of Cr(CO) . 

To study the impact of biogenic sources of hydrocarbons on gas phase photochemistry in the atmosphere, new isotopic ratio-based techniques are required. For example, ultra-high volume collection of aldehydes with separation of formaldehyde and acetaldehyde (or their derivatives), and subsequent 3q an[Pg.278]

Therefore, gas phase photochemistry of inorganic and simple organic gases may have contributed to the prebiotic synthesis of organic materials, which subsequently may have been building blocks for animate matter [19]. 

In contrast to gas-phase photochemistry, aqueous-phase and solid-phase photochemistry are treated differently. For example, the Beer-Lambert Law for homogenous liquid systems is expressed simply as ... 

The most common units used in gas phase photochemistry for concentration are number of molecules cm-3 symbolised by N with natural logarithms. The gas phase absorption coefficient designated, o, is then in units of cm2 molecule 1, a is also known as absorption cross-section. The Beer-Lambert law becomes... 

On the other hand, physicists usually use the number of absorbing molecules N per cm in gas phase photochemistry instead of the pressure p of the absorbing gas component leading to Eq. 3-7. 

Fig. 6.12 Comparison of photochemistry and quantum yields of hydrogen peroxide and of ozone gas phase photochemistry of O3 see text.

General features of primary processes important in the gas-phase photochemistry of simple carbonyl compounds have been described by Calvert and Pitts (46) and Cundall and Davies (61). 

Gas-phase photochemistry of Fe(CO)s has been carried out at three wavelengths, 351, 248, and 193 nm. At 351 mn Fe(CO)4 and Fe(CO)3 are produced while at 248 mn Fe(CO)2 is also observed. The gas-phase structures of these materials were determined by comparison of their IR spectra with those in condensed phases. At 193 nm, a new species believed... 

Gas-phase photochemistry of W(CO)6 at 355 nm yields W(CO)s. The reactions of this species with NH3, C2H6, CF4, SFe, and Xe were examined. NH3 and C2H6 form stable species under these conditions while Xe formed an unstable species. Neither CF4 nor SFe formed complexes. ... 

It is a pleasure to welcome Dr. Baggott to the team of Reporters. This year, the volume of significant publications in the field of gas-phase photochemistry seems to have increased markedly, and the 1083 references in his review compare with 898 in Volume 14. This large increase has necessitated a change in the method of presentation much of the work is mentioned briefly in tabular form, and only that regarded as particularly notable is discussed in the main text. 

J. C. Whitehead, Ed., Selectivity in Chemical Reactions (Kluwer Acaidemic Publishers, Dordrecht, 1991) M. N. R. Ashfold and J. E. Baggott, Eds., Advances in Gas-Phase Photochemistry and Kinetics, Bimolecular Collisions (Royal Society of Chemistry, London, 1989) J. Jortner, R. D. Levine and B. Pulman, Eds., Mode Selective Chemistry (Kluwer Acaidemic Publishers, Dordrecht, 1991). 

It is beyond the scope of this book to review gas phase photochemistry in any detail. We restrict ourselves to a limited discussion of the origin of some of the reactants of relevance in atmospheric water. 

The gas-phase photochemistry of haiogenated ethenes has been studied in the UV and VUV [60, 61], as well as in the infrared, using multiple-photon-absorption excitation with powerful CO2 laser sources [62-66]. Also, sensitized decompositions, for example using electronically excited Hg( P) atoms, have also been reported [67-69]. The net gas-phase photochemistry of these systems usually involves hydrogen halide elimination via three-and/or four-center transition states, with some evidence for simple bond fission producing halogen atoms in the case of Hgf Pj) photosensitization [70]. 

The purpose of this article is the presentation of a summary of the contributions that have been made to our understanding of the gas phase photochemistry of the simple oxides and sulfides of carbon. An effort has been made to cover the published accounts of research in the English language literature through December 1974. 

Physical and chemical evolution of target aerosol system in isolation and externally-mixed with a different seed background aerosol population with gas phase photochemistry. 

It may be appreciated that the introduction of gas phase photochemistry into systems such as described above will introduce a range of complications of atmospheric importance. 

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