The spectroscopy , or spectrometry , is the study of the spectrum of a phenomenon, i.e. the study of the distribution of a wave or a beam of particles according to the frequency or of energy.

The suffix “- radioscopy” refers to the visual observation, for example the impression on a photographic film, projection on a screen or the use of glasses of observation (for example glasses assembled on a Goniomètre for the dispersion of the light by a prism). The suffix “- metry” refers to the recording of a signal by an apparatus (tracing Table or electronic recording).

This size can be a electromagnetic Rayonnement, but also a mechanical Onde like the its or the seismic waves, or of the particle S or the masses. The Measuring instrument making it possible to obtain a spectrum is a Spectromètre .

The spectroscopy is used in many fields: Astronomy, Biophysics, Chemistry, Physical atomic, Nuclear physics, solid state Physics…

There exist various types of spectroscopies classified according to the measured physical size or the process of the measurement.

Concept of spectrum

See also: spectral Analysis

The visible Lumière, when it “is dispersed” by a prism or a Diffraction pattern, reveals its composition or spectrum. The Arc-en-ciel is the most known illustration, obtained by the dispersion of a Lumière, that of the Sun, by the drops of Eau of the Pluie playing the part of centrifugal spreader in direction of the sunlight: each Color or Frequency share in a different direction.

One sees thus that the Lumière can be broken up several colors, and than it is this “proportioning” between the various colors which gives the final color.

When an instrument plays a Its musical, this sound comprises several harmonic, and the Oreille exerted of a Musicien can detect several heights there; for example if a Piano plays a C, one will hear in a weak way C with the higher octave, then a acuter ground, then still C… It is the proportioning between these harmonics which amongst other things characterizes the stamp of the instrument. All the sounds thus include/understand a series of Partiel S or Harmonique S, which defines its main features (height, intensity, sonority,…), visualized since the beginning of the century by an apparatus called Sonagraphe, apparatus which gives an about exact representation of the sound Specter , evolutionary.

But the concept of spectrum is more general. Let us take for example a flood of Automobile S on a road. One can determine the number N ( X ) of cars being in a band of 100  m around the kilometric point X , it is the density of circulation. One can also determine the number NR ( v ) of cars having a speed v , some is their position on the road. One can say that NR is the spectrum of speed of the density of circulation N ; they are in two ways complementary to describe the same object.

In a general way, one can speak about spectrum when one has two variable dual, i.e. when a function ƒ of a variable X can break up into a succession of functions G dependant on a parameter multiplied by a function has there, has depend on the product X · there :

$f\; (X)\; =\; \backslash \; sum\_y\; G\; (there)\; \backslash \; cdot\; has\; (there\; \backslash \; cdot\; X)$ is $f\; (X)\; =\; G\; (1)\; \backslash \; cdot\; has\; (X)\; +\; G\; (2)\; \backslash \; cdot\; has\; (2x)\; +\; G\; (3)\; \backslash \; cdot\; has\; (3x)\dots$

or in a more general way

$f\; (X)\; =\; \backslash \; int\_y\; G\; (there)\; \backslash \; cdot\; has\; (there\; \backslash \; cdot\; X)\; \backslash \; cdot\; dy$

has ( X ) being a standard function; in physics, one considers in general only functions sine oïdales or Exponentielle S complexes for has ( X ), for example

$a\; (X)\; =\; \backslash \; cos\; \backslash \; left\; (X\; \backslash \; frac\; \{2\; \backslash \; pi\}\; \{T\}\; \backslash \; right)$ or $e^\; \{-\; J\; X\; \backslash \; frac\; \{2\; \backslash \; pi\}\; \{T\}\}$.

J being the imaginary noted I in mathematics.

The passage of ƒ with G is called “development in Fourier series” when it is about a discrete continuation ( there taking whole values ), and “Transformée of Fourier” when it is about a function continues there .

In Physical, one is often interested in the spectrum in energy ( there = E ), i.e. with the number of particles having a given energy E ; or, one is interested in dual variables whose product is energy ( X · there = E ). But it is not systematic.

Electromagnetic spectrum

See also: electromagnetic Spectrum

Each object has a characteristic color which is the result of the light not absorptive by the Molécule S which compose it; thus the Chimie was born from the production from dyes or pure Molécule S by Chromatographie, which is art to separate the molecules by physically dispersing them by Capillarité or diffusion. It is of course necessary to light the Molécule with Lumière.

One thus manages to consider that the Lumière consists of a superposition of waves Monochromatique S having intensities well defined according to the frequency. One can then, in theory, reconstitute a light when his spectrum is known, it is necessary for that to succeed in superimposing waves Monochromatique S having the intensity indicated by the spectral curve: the luminous intensity I according to the frequency ν: I (ν). The mathematicians express that by saying that the function ƒ ( X , T ) can be expressed in a base of functions and that is written

$F\; (X,\; T)\; =\; \backslash \; int\; \backslash ;\; I\; (\backslash \; Omega)\; e^\; \{J\; (\backslash \; Omega\; \backslash \; cdot\; T\; -\; K\; \backslash \; cdot\; X)\}\; dt\; \backslash ;$

where ω = 2π·ν and K = 2π/λ. In the case of the electromagnetic waves, ƒ is either the vector of the electric field, or the vector of the magnetic field (both being narrowly bound by the Maxwell's equations) in a given point.

The spectrum can be described by a function of the variable energy or Fréquence (sizes connected by the equation of Planck ( E = H ·ν) where H is a fundamental constant of physics called Constante of Planck.

Various types of spectroscopy

The type of spectroscopy depends on the type of measured object. The three following classes are distinguished:

• the emitted or absorptive electromagnetic radiations which are studied by the electromagnetic Spectroscopie.

• the macroscopic vibrations of a medium which are studied by the acoustic Spectroscopie and the dynamic mechanical Spectroscopie.
• the ions accelerated in an electromagnetic field which are studied by the Spectrometry mass.

In the case of the electromagnetic radiations, the analyzed spectrum can be:

• a spectrum emitted by the object to analyze, one speaks about Spectrométrie of emission; this spectrum has in general:
• a continuous part: it is the thermal radiation of origin called “radiation of the black Corps”; this radiation makes it possible to determine the Température object;
• a discrete part: the emission lines characteristic of the atoms;
• a spectrum emitted by a source (a lamp) and modified by the object to analyze, one speaks about Spectrométrie of absorption; this spectrum is in general a “grooved spectrum” it acts of a continuous spectrum, coming from the source, and presenting “holes”, the absorption lines characteristic.

Process of measurement

Various types of spectroscopy use varied processes.

Spectroscopy by x-rays

See also: Spectrometry of x-ray fluorescence

When the X-rays of a Fréquence (energy) sufficient interact with a substance, the electron S of the internal layers excited towards external orbits, or are ejected (photoelectric Effet). The de-energizing of the Atome occurs according to two processes: the Fluorescence or the emission Auger. The Frequency S of absorption and emission are characteristic of a Atome.

Spectroscopy of x-rays

In Astronomy, one makes also spectroscopy of x-rays emitted by the star S, the Galaxie S etc the technique used is that which consists in recording the energy of each Photon emitted in a range of energy given. It is the satellite case of like INTEGRAL. The technological prowess consisting in making converge rays of high energy as in traditional optics was successful with the satellite Chandra. In this case, the Photon S are deflected by incidence shaving on special Miroir S.

X-ray crystallography

See also: X-ray crystallography

Crystallography with x-rays, or X-ray crystallography, is a process in which the crystals are lit by a beam of x-rays under a certain angle; one can obtain similar figures with a beam of electron S or of Neutron S. the measurement of the Diffraction of the x-rays on the Cristal makes it possible to know the mesh sizes crystalline. The structure of the crystal can be given by combining all information.

It is here about a spectrum in distances interréticulaires: the initial variable is the position of the Atome in the unit cell, the dual variable, that which is determined by the diffractogram, is the distance separating the crystallographic plans. To be more rigorous: the initial variable is the Fonction of wave electronic cloud, the figure of diffraction is a transform of Fourier of this function of wave (see the Physics article solid state ).

However, this method is seldom regarded as a spectroscopic method, although the diffractogram is sometimes called “spectrum of diffraction”.

Visible spectroscopy

Many atoms emit or absorb the visible Lumière. In order to obtain a spectrum according to a fine line, or “stripes”, the atoms must be in a gas phase. That means that the substance must be vaporized. The spectrum is studied in absorption and emission.

Spectroscopy UV

The Atome S absorb or emit in the area of the Ultraviolet S. In fact the external layers of the electronic cloud are implied in this process. The Molécule S also absorb the visible radiation Ultraviolet and : the absorption of a photon Ultraviolet can cause the promotion of an electron of a molecular Orbitale flexible or not-flexible in orbital anti-flexible, typically of HOMO in the LUMO.

Spectrometry of electrons

Spectrometry by deviation is a simple method to measure the spectrum of a beam of electron S, is to make pass this one in a Magnetic field constant and uniform. Each electron will be deviated of an angle dependant on kinetic sound energy, which makes it possible to acquire the spectrum, for example, on a photo plate.

Mass spectrometry

See also: Spectrometry mass

It is a question of determining the Masse S (and to possibly have information on the chemical structure) of the Molécule S of which the sample is made up, by ionizing them and by measuring their report/ratio/load (m/Z) masses. The concept of “spectrum in mass” is rather different from that of spectrum of a signal, but it is a question well of determining the distribution of a value (how much particles have a given mass) of a system.

Astronomical spectroscopy

See also: astronomical Spectroscopy

In Astronomie the spectroscopy is a technique largely used as well in UV, optics and the infra-red. One distinguishes:

• the Spectroscopy long-slit which uses the first orders of diffraction and is used generally for the spectroscopy of only one object at the same time

• the Spectroscopie scale which uses the high orders of diffraction, and which makes it possible to reach very high spectral resolutions
• the Spectroscopie multi-objects which is dedicated to the simultaneous spectroscopy several objects at the same time, either thanks to masks, or thanks to fiberoptics.

Combined spectroscopy

• Transformed of Fourier for the Infra-red when the conditions change with time (FTIR)

• Microscope with atomic force
• dielectric Spectroscopie

See too

• Raman Spectrometry

• Spectrometer
• Spectrometer Mössbauer
• astronomical Spectrofluorimètre
• Spectroscopy
• Spectroscopy scale
• Spectroscopy long-slit
• Spectroscopy near infra-red
• Spectrometry to x-ray fluorescence
• spectral Signature
• Biophysics
• Gun plasma (chemistry)
• Interaction radiation-matter
• Microsounder of Castaing
• ferromagnetic Resonance
• Spectrometry of loss of energy of the electrons (EELS)

External bonds

Count of the numbers of wave of the vibrations of valence and deformation

Simple: Spectroscopy

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