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The fundamental transitions give rise to absorption in the mid-infrared in the regions around 1650 cm −1 (μ band, 6 μm) and 3500 cm −1 (so-called X band, 2.9 μm) Electronic transitions in which a molecule is promoted to an excited electronic state. The lowest energy transition of this type is in the vacuum ultraviolet region.
The higher energy (shortest wavelength) ranges of UV (called "vacuum UV") are absorbed by nitrogen and, at longer wavelengths, by simple diatomic oxygen in the air. Most of the UV in the mid-range of energy is blocked by the ozone layer, which absorbs strongly in the important 200–315 nm range, the lower energy part of which is too long for ...
By recording the attenuation of light for various wavelengths, an absorption spectrum can be obtained. In physics, absorption of electromagnetic radiation is how matter (typically electrons bound in atoms) takes up a photon's energy—and so transforms electromagnetic energy into internal energy of the absorber (for example, thermal energy). [1]
The energy required for this is always larger than about 10 electron volt (eV) corresponding with wavelengths smaller than 124 nm (some sources suggest a more realistic cutoff of 33 eV, which is the energy required to ionize water). This high end of the ultraviolet spectrum with energies in the approximate ionization range, is sometimes called ...
The visible band sits adjacent to the infrared (with longer wavelengths and lower frequencies) and the ultraviolet (with shorter wavelengths and higher frequencies), called collectively optical radiation. [2] [3] In physics, the term "light" may refer more broadly to electromagnetic radiation of any wavelength, whether visible or not.
Electromagnetic radiation in this range of wavelengths is called visible light (or simply light). The optical spectrum is sometimes considered to be the same as the visible spectrum, but some authors define the term more broadly, to include the ultraviolet and infrared parts of the electromagnetic spectrum as well, known collectively as optical ...
Water absorbs the warmer long wavelengths colours, like reds and oranges, and scatter the cooler short wavelength colours. [11] Most of the solar energy reaching the Earth is in the range of visible light, with wavelengths between about 400-700 nm. Each colour of visible light has a unique wavelength, and together they make up white light.
Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those of red light (the longest waves in the visible spectrum ), so IR is invisible to the human eye.