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Spectral line

Dark or bright lines in a uniform continuous spectrum

This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Spectral lines are uniform and continuous spectrum A dark or bright line in the, due to the emission or absorption of light in a narrow frequency range compared to the nearby frequency. Spectral lines are usually used to identify atoms and molecules from their characteristic spectral lines. Because Electronic cloud The electrons in are circling Nucleus When the electron energy changes, this energy difference will produce atom Idiosyncratic photon This is the origin of spectral lines.

Chinese name: Spectral line
Foreign name: spectral lines
Power: Energy difference

influence factor: electric field and magnetic field
Purpose: Identification of Atoms and Molecules by Characteristic Spectra
Classification: Absorption spectrum, emission spectrum

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seven Application examples

definition

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Spectral lines are uniform and continuous spectrum A dark or bright line in the, due to the emission or absorption of light in a narrow frequency range compared to the nearby frequency.

Cause

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The spectral line is quantum The result of the interaction between a system (usually an atom, but sometimes a molecule or nucleus) and a single photon. When photon Photons are absorbed when there is appropriate energy to allow the system to produce energy state changes (in the case of atoms, this is usually the orbit of electron changes).^[1] Then, it will spontaneously re emit, or cascade at the same frequency as the original frequency, where the total energy of emitted photons will be equal to the energy of absorbed photons (assuming that the system returns to its original state).

classification

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Spectral lines are divided into emission spectrum or absorption spectrum. Which type of spectral line depends on the type of material and its temperature relative to another emission source.

Generated when photons from a hot, broad spectrum source pass through a cold material absorption spectrum 。 The light intensity in the narrow frequency range decreases due to the absorption of the material and the re emission in the random direction.

Absorption line

Conversely, when photons from hot materials are detected in the presence of a broad spectrum from a cold source, a bright emission spectrum is generated. The intensity of light in a narrow frequency range increases due to the emission of the material.

emission spectrum

name

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The strong spectral lines in the visible part of the spectrum usually have unique names, such as ionization K of the line at 393.366 nm appears in Ca+, although some spectral "lines" are blends of multiple lines from several different species.

In other cases, according to the ionization level, the line is specified by adding Roman numerals to the name of the chemical element, so that Ca+also has the name Ca II. Neutral atoms are represented by the Roman number I, single ionized atoms are represented by II, and so on, so that for example, Fe IX (IX, Rome 9)

Atomic hydrogen spectroscopy Lines also have assigned names within their respective series, such as Lyman series or Balmer series.

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Identify chemical composition

Spectral lines are highly atom specific and can be used to identify the chemical composition of any medium (usually gas) through which light passes. Several elements, such as helium, thallium and cerium, were discovered by spectroscopic means.

Analysis of astrochemical composition

Spectral lines also depend on the physical conditions of gases, so they are widely used to determine the chemical composition of stars and other celestial bodies that cannot be analyzed by other means of physical conditions.

Factors affecting spectral lines

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The presence of specific spectral lines indicates the existence of certain elements. The content of this element can be measured by the intensity of the spectral line. If the spectral line has displacement , then pass Doppler effect The moving speed of the light source towards or away from the observer can also be obtained.

Atomic motion

The movement of atoms (whose speed is related to temperature) will cause Line broadening The reason is that part of the movement is toward the observer, while part of the movement is far away from the observer, so the temperature can be obtained from the width of the spectral line. The density can be determined by the intensity or width of several different spectral lines.

Electric and magnetic fields

In addition, join electric field and magnetic field If the effect is strong enough, it will also affect the shape of the spectral line.

Causes of broadening atomic spectral lines

Several reasons for the broadening of atomic spectral lines are theoretically given, namely: ① Natural lineweight It is the intrinsic property of the atom (that is, it is involved in the transition energy level Characteristics); ② Doppler broadening , which is the result of the irregular thermal movement of atoms; ③ Collision broadening, which is the result of the interaction between atoms, has been estimated on the order of magnitude for these reasons. It has reference significance for the determination of atomic spectrum

Application examples

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1. Study on atomic and ionic spectral lines produced by laser ablation of copper

The spectral lines induced by Nd ∶ YAG pulsed laser ablation of metal Cu and their intensity distributions with time and space were measured Plasma radiation The spectral line is composed of atomic spectral line, ion spectral line and continuous radiation background light. The number of Cu atomic spectral line is not only more than that of ion spectral line, but also the radiation intensity is greater than that of ion spectral line. The radiation intensity of continuous radiation background light is the weakest; The emission range of atomic spectral line is the largest and the duration is the longest; The emission range of ion spectral line is medium and the duration is medium long; The continuous radiation background light has the smallest luminous range and the shortest duration. The mechanism of laser induced luminescence is discussed. It is believed that the continuous radiation background light in the plasma plume mainly comes from the bremsstrahlung of high-energy electrons near the target and the combined excitation of electrons and ions. The atomic and ion spectral lines are mainly caused by the collisional energy transfer excitation of high-energy electrons in the plasma, The observed experimental phenomena are well explained·^[2]

2. Study on soil spectral lines in china

The analysis of soil spectral reflectance across China shows that no matter in two-dimensional or multi-dimensional space, there is indeed a soil spectral line, but it is not a strict straight line, but a band with appropriate width. It is not suitable to use a national unified soil spectral line for vegetation analysis. The errors of different soil spectral lines in the estimation of greenness and vegetation coverage were discussed. The results of principal component analysis of soil spectral reflectance and its physical significance are also discussed.^[3]

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