Photodissociation of oxygen

Reactions with molecular species above the arrow e.g. RIO) involve subsequent reactions with these species to produce the indicated products. In most cases the reactants shown to the left of the arrow participate in the slowest or rate-determining step]. The CH3O radical formed in Rll then follows reaction R7. The H02 radical formed in RIO is the other member of the family and is linked with HO in a variety of chain reactions. These radicals are produced following HO attack on hydrocarbons or by photodissociation of oxygenated hydrocarbons such as formaldehyde (RIO) and acetaldehyde ... 

B. Atomspheric photochemistry. The photodissociation of oxygen in sunlight is the major photochemical process occurring in earth s atmosphere. The first intense allowed transition in O., is B - X 32 which occurs at 202.6 nm and is called the Schumann-Runge band system (Section 2.8). It merges intoa continuum beyond 175.9 nm and correlates with one oxygen atom 0(23P) in the ground state and one in the excited state O (2 D)... 

The atmospheric conditions and the rates of the various reactions for which measured laboratory values are available indicate that the maximum rate of photodissociation of oxygen occurs in the stratosphere, and results in a maximum concentration of ozone also in the stratosphere at about 25 km.3 Detailed studies show that the ozone is in photochemical equilibrium at levels above that of its maximum concentration. In other words, the production of ozone by solar ultraviolet radiation is automatically compensated by the re-formation of oxygen molecules in the upper stratosphere where equations (8) and (9) can be applied. 

Photodissociation Photodissociation is a process in which high-energy ultraviolet solar radiation is absorbed by molecules, causing their chemical bonds to break. In the upper atmosphere, the photodissociation of oxygen absorbs much of the high-energy UV radiation and produces atomic oxygen. 

The amount of ozone in the stratosphere is determined by a dynamic balance between the processes of production and destruction. Ozone is formed by a two stage process that begins with photodissociation of oxygen by wavelengths < 242 nm... 

Orii Y, Webster DA (1986) Photodissociation of oxygenated cytochrome o (s) (Vitreoscilla) and kinetic studies of reassociation. J Biol Chem 261 3544-3547 Oro J (1994) Early chemical stages in the origin of life. In Bengtson S (ed) Early life on Earth. 

Siskind, D.E., K. Minschwaner, and R.S. tick man, Photodissociation of oxygen and water vapor in the middle atmosphere Comparison of numerical methods and impact on modeled ozone and hydroxyl. Geophys Res Lett 21, 863, 1994. 

As mentioned earlier, ozone in the stratosphere prevents UV radiation emitted by the snn from reaching Earth s surface. The formation of ozone in this region begins with the photodissociation of oxygen molecules by solar radiation at wavelengths below 240 nm ... 

Instead of a time constant for the approach to steady state one may also consider the time required to replenish the average amount of ozone observed at a given altitude by the photodissociation of oxygen. This... 

Niwa, A. Matsuzaki, S. Nishio, and H. Sato, Ozone formation by photodissociation of oxygen molecule with a 193 nm excimer laser, J. Phys. Chem. A 101(4), 668 671 (1997). 

Ozone also decomposes to form an oxygen atom that is also a powerful oxidizing agent. Ozone is prepared either by the photodissociation of oxygen (O2)... 

Schematic presentation of reaction paths in photodissociation of oxygen protonated formamide. MXSwh/ MXSco/ and MXScw denote minima on the crossing seam for dissociation of N-H, C=0, and C-N bond, respectively. Geometries are optimized at the CASSCF(10,8)/6-31G(d) level (Data from Antol et al. 2008b)...

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