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Photochemical immersion well reactor (50 mL) with a mercury-vapor lamp.. Photochemistry is the branch of chemistry concerned with the chemical effects of light. Generally, this term is used to describe a chemical reaction caused by absorption of ultraviolet (wavelength from 100 to 400 nm), visible (400–750 nm), or infrared radiation (750–2500 nm).
Photooxygenation reactions are initiated by a photosensitizer, which is a molecule that enters an excited state when exposed to light of a specific wavelength (e.g. dyes and pigments). The excited sensitizer then reacts with either a substrate or ground state molecular oxygen, starting a cascade of energy transfers that ultimately result in an ...
The relationship between energy and wavelength is determined by the Planck-Einstein relation = = where E is the energy of the quantum , f is the frequency of the light wave, h is the Planck constant, λ is the wavelength and c is the speed of light.
As polarised light passes through a birefringent sample, the phase difference between the fast and slow directions varies with the thickness, and wavelength of light used. The optical path difference (o.p.d.) is defined as o . p . d . = Δ n ⋅ t {\displaystyle {o.p.d.}=\Delta \,n\cdot t} , where t is the thickness of the sample.
Wavelengths of electromagnetic radiation, whatever medium they are traveling through, are usually quoted in terms of the vacuum wavelength, although this is not always explicitly stated. Generally, electromagnetic radiation is classified by wavelength into radio wave, microwave, infrared, visible light, ultraviolet, X-rays and gamma rays. The ...
Woodward's rules, named after Robert Burns Woodward and also known as Woodward–Fieser rules (for Louis Fieser) are several sets of empirically derived rules which attempt to predict the wavelength of the absorption maximum (λ max) in an ultraviolet–visible spectrum of a given compound.
The theory of light-matter interaction on which Cauchy based this equation was later found to be incorrect. In particular, the equation is only valid for regions of normal dispersion in the visible wavelength region. In the infrared, the equation becomes inaccurate, and it cannot represent regions of anomalous dispersion. Despite this, its ...
However, because short-wavelength photons carry more energy per photon, the maximum amount of photosynthesis per incident unit of energy is at a longer wavelength, around 650 nm (deep red). It has been noted that there is considerable misunderstanding over the effect of light quality on plant growth.