Spectroscopy

Spectroscopy is a set of methods to analyze the energy spectrum of a sample by radiation is divided according to their energy. For visual observation of optical spectra are used spectroscopes, hot -recording devices spectrometer. The latter work also in other regions of the electromagnetic spectrum, as well as particles such as electrons or ions. The excitation of the sample can be accomplished with a type of radiation and other transmission of the specimen to be examined.

Already in 1814 Joseph von Fraunhofer discovered dark lines in the spectrum of the sun, the Fraunhofer lines, without being able to explain their origin. Gustav Robert Kirchhoff in 1859 found and Robert Wilhelm Bunsen, that different chemical elements color the flame of a gas burner in a characteristic way. This type of application is aimed at, the composition of the sample. If then quantitative measurements, often of concentrations, but also other physical quantities such as pressure or electric or magnetic fields, it is called spectrometry. These include methods in a broader sense, in which not resolved by the energy, but after about the mass of particles, see mass spectrometry.

Often, however, it goes straight to the energy spectrum itself so gave spectroscopic observations decisive impetus to the development of quantum mechanics and provide information on the chemical structure of unknown substances. The precision with which some spectral lines can be measured, allowing the determination of fundamental constants, the testing of hypotheses about the laws of nature and the definition of the base units meter and second.

• 6.1 General Textbooks
• 6.2 Special works

Physical Basics

A spectrum for the purposes of this article is the application of a spectral power density over an energy scale (frequency, wave number ) or a reciprocal energy scale. The relationship between the frequency of an electromagnetic wave and the energy of the photons is given by

With Planck's constant.

Basis for the understanding of spectra ( without resorting to actually formally correct orbital model) is the Bohr model of the atom. This can explain the absorption and emission of photons by transitions between different energy levels of an atom. The absorbed or emitted energy is determined by the initial energy level and the final energy level. In quantum mechanics, this is called energy levels as a state.

The following applies:

Is the difference so positive, so it is in this example, emission, and negative sign, so then to absorption.

Structures in the spectrum give evidence which amounts of energy to record a substance ( absorb ) or release ( emit ) can. These amounts correspond to energy differences of quantum-mechanical states of the sample. The spectrum of a substance depends in particular on the concentrations of selection rules and occupation numbers.

Classical spectroscopy

The study of the light emission or absorption of molecules and atoms by lattice and prism spectrometers are the oldest spectroscopic methods. They are therefore also referred to as classical spectroscopy. Many of the basic research on the structure of the atom was made ​​possible by the development and application of high-resolution grating and prism spectrometers.

Types of spectroscopy

Classification

The classification of various spectroscopic methods and procedures is varied and not always consistent in the literature. Generally these first of all methods of atomic and molecular spectroscopy. Atomic spectroscopy includes spectroscopic methods, which go back to emission, absorption or fluorescence processes in atoms and are used for the determination of chemical elements. The observed spectra are generally line spectra. The molecular spectroscopy methods, however, are based on the excitation and analysis of rotational, vibrational and electronic states in molecules. There is no line spectra but so-called band spectra are observed by the superposition of individual states.

Beyond this basic classification, according to the nature of the studied states, there are numerous other subdivisions, for example, after the excitation energy of the electric radiation (eg, microwave spectroscopy, X-ray spectroscopy ), the physical state (eg, solid state spectroscopy ) or the type of excitation ( electron spectroscopy, for example, laser spectroscopy).

List of types of spectroscopy and methods in analysis

• Atomic Absorption Spectroscopy ( AAS / OAS) flame technique
• Graphite furnace technique
• Hydride

• Inductively coupled plasma (ICP -OES)
• Microwave plasma torch -AES ( MPT -AES)

• Photoelectron spectroscopy with X-rays ( XPS)
• Photoelectron spectroscopy with UV light ( UPS )
• Angle-resolved photoelectron spectroscopy ( ARPES )
• Auger electron spectroscopy (AES)
• Electron energy loss spectroscopy ( EELS)

• X-ray fluorescence analysis (XRF )
• X-ray diffraction ( XRD)
• X-ray absorption spectroscopy ( XAS )

• Frequency modulation spectroscopy
• Fluorescence spectroscopy Single -molecule fluorescence spectroscopy
• Fluorescence correlation spectroscopy,

• Infrared spectroscopy (IR)
• Raman spectroscopy

• Electron-nuclear double resonance ( ENDOR )

• Absorption or transmission spectroscopy
• Reflectance spectroscopy
• Photo line spectroscopy

• Cavity ring-down spectroscopy ( CRDS also CRLAS )
• Laser-induced fluorescence (LIF)
• Ultrafast Spectroscopy - Measurements of the details of fast processes, especially chemical reactions

Spectroscopy in Astronomy

The element helium was - first recognized by spectroscopic investigations of sunlight - long before detection on Earth. A spectral line in the solar spectrum could not be assigned to laboratory chemical substance, so that had to exist an unknown element on the sun.

More classic successes of astronomical spectral analysis are

• The detection of the Doppler effect of stars (see radial velocity )
• And ( 1920 ) on galaxies ( see redshift ),
• Of magnetic fields on the Sun and bright stars ( Zeeman effect )
• And especially the determination of stellar temperatures and the spectral classes (see Hertzsprung -Russell diagram and stellar evolution ).

The associated measuring instruments (" Spectroscopic ") of the Astro spectroscopy are:

• The spectroscope and the spectrometer (both visual)
• The spectrograph (photographic or sensors )
• The monochromator and the interference spectrometer
• The frequency comb