Absorption spectroscopy

Absorption spectroscopy refers to a range of techniques employing the interaction of electromagnetic radiation with matter. (chemistry.) In absorption spectroscopy, the intensity of a beam of light of measured before and after interaction with a sample is compared. When combined with the word spectroscopy, the words transmission and remission refer to the direction of travel of the beam measured after absorption to that before. The descriptions of the experimental arrangement usually assume that there is a unique direction of light incident upon the sample, and that a plane perpendicular to this direction passes through the sample. Light that is scattered from the sample toward a detector on the opposite side of the sample is said to be detected in transmission and treated according to the theory of transmission spectroscopy. Light that is scattered from the sample toward a detector on the same side of the sample is said to be detected in remission and it is this light that is the subject of remission spectroscopy. The remitted radiation may be composed of two kinds of radiation referred to as specular reflection (when the angle of reflection is equal to the angle of incidence) and diffuse reflection (at all other angles).

Another descriptor associated with absorption spectroscopy is the wavelength range of the radiation being used in the incident beam. Thus you will find references to UV-visible spectroscopy.

UV-visible spectroscopy refers to techniques where one measures how much sunlight is dangerous) so the amount of DNA in a sample can be determined by measuring the absorbance of UV light.

The relation between the visible color and the absorbance color is complicated; a sample that appears red does not absorb in the red, but absorbs at OTHER wavelengths (colors) so that the light which passes through the sample is enriched in red.

The word "color" is placed in quotes to indicate that absorbance spectroscopy deals not only with light in the visible range - photons with a wavelength of roughly 400 to 700 nanometers, but also with wavelengths that lie outside of the range of human vision (IR, UV, X-rays). However, the principles are quite similar for both visible and nonvisible light.

More technically ^{[1] [2]}, absorption spectroscopy is based on the absorption of photons by one or more substances present in a sample, which can be a molecules.

While the relative intensity of the absorption lines do not vary with concentration, at any given wavelength the measured absorbance ( − log(I / I₀)) has been shown to be proportional to the radiation absorbed, one can determine the structure and concentration of the compound.

Visible light absorption spectra can be taken in anything that is visibly clear. ionic, do not have significant IR absorptions, and Nujol has a relatively uncomplicated IR spectrum.