Spectra presentation. Spectral analysis. Spectral devices. Types of radiation and spectra Spectrum and spectral devices presentation
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Classification of spectral instruments.
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Spectral devices are called devices in which light is decomposed into wavelengths and the spectrum is recorded. There are many different spectral instruments, differing from each other in registration methods and analytical capabilities.
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When choosing a light source, care must be taken to ensure that the resulting radiation is effectively used for analysis. This is achieved the right choice spectral instrument
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There are filter and dispersive spectral devices. In filters, a narrow wavelength range is highlighted with a light filter. In dispersive - the radiation of the source is decomposed into wavelengths in a dispersing element - a prism or a diffraction grating. Filter instruments are used only for quantitative analysis, dispersion instruments are used for qualitative and quantitative
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Distinguish between visual, photographic and photoelectric spectral devices. Styloscopes - devices with visual registration, Spectrographs - devices with photographic registration. Spectrometers are devices with photoelectric recording. Filter devices - with photoelectric registration. In spectrometers, decomposition into a spectrum - in a monochromator, or in a polychromator. Monochromator-based instruments are called single-channel spectrometers. Devices based on a polychromator - multichannel spectrometers.
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All dispersive devices are based on the same basic diagram. Devices may differ in the registration method and optical characteristics, they may have different appearance and design, but the principle of their operation is always the same. The schematic diagram of a spectral device. S- entrance slit, L 1- collimator lens, L 2- focusing lens, D- dispersing element, R- recording device.
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S L 1 D L 2 R Light from the source enters the spectral device through a narrow slit and from each point of this slit in the form of diverging beams falls on the collimator lens, which converts diverging beams into parallel ones. The slit and the collimator lens make up the collimator part of the device. Parallel beams from the collimator objective fall on a dispersing element - a prism or a diffraction grating, where they are decomposed into wavelengths. From the dispersing element, light of one wavelength coming from one point of the slit comes out in a parallel beam and hits the focusing lens, which collects each parallel beam at a certain point of its focal surface - on a recording device. Numerous monochromatic images of the slit are composed of individual points. If the light is emitted by individual atoms, then a series of separate images of the slit in the form of narrow lines is obtained - a line spectrum. The number of lines depends on the complexity of the spectrum of the emitting elements and the conditions for their excitation. If individual molecules are shining in the source, then the lines close in wavelength are collected in bands, forming a striped spectrum. The principle of operation of the spectral device.
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slot purpose
R S Entrance slit - object of the image Spectral line - monochromatic image of the slit, built with the help of lenses.
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lenses
L 2 L 1 lenses spherical mirrors
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Collimator lens
S F О L1 The slit is located in the focal surface of the collimator objective. After the collimator lens - from each point of the slit, the light comes in a parallel beam.
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Focusing lens
Spectral line F О L2 Draws an image of each point of the slit. From points it is formed. slit image - spectral line.
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dispersing element
D Dispersive prism diffraction grating
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Dispersing prism ABCD - prism base, ABEF and FECD - refractive edges, Between refractive edges - refractive angle EF - refractive edge.
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Dispersing prism types
60 degree prism Cornu quartz prism; 30 degree mirrored prism;
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rotary prisms
Rotary prisms play a supporting role. They do not decompose the radiation into wavelengths, but only rotate it, making the device more compact. Turn 900 Turn 1800
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combined prism
The constant deflection prism consists of two thirty-degree dispersing prisms and one rotary prism.
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Monochromatic beam path in a prism
i In the prism, the light beam is twice refracted at the refractive faces and exits from it, deviating from the original direction by an angle of deflection . The deflection angle depends on the angle of incidence i and the wavelength of the light. At a certain i, the light passes through the prism parallel to the base, the deflection angle is minimal; in this case, the prism works under the conditions of the smallest deflection.
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Ray path in a prism
2 1 1 2 The decomposition of light occurs due to the fact that light of different wavelengths is refracted in a prism in different ways. Each wavelength has its own deflection angle.
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Angular dispersion
1 2 Angular dispersion B is a measure of the efficiency of wavelength decomposition of light in a prism. Angular dispersion shows how much the angle between two adjacent beams changes with wavelength:
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Dependence of dispersion on the material of the prism quartz glass
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Angular dispersion versus refractive angle
glass glass
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Contents Types of radiation Light sources Spectra Spectral devices Types of spectra Spectral analysis
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Types of radiation Thermal radiation Electroluminescence Chemiluminescence Photoluminescence Content
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Thermal radiation The simplest and most widespread type of radiation is thermal radiation, in which the energy losses by atoms for the emission of light are compensated for by the energy of the thermal motion of atoms (or molecules) of the emitting body. The higher the body temperature, the faster the atoms move. When fast atoms (or molecules) collide with each other, part of their kinetic energy is converted into the excitation energy of atoms, which then emit light. The heat source of radiation is the sun, as well as an ordinary incandescent lamp. The lamp is a very convenient but low-cost source. Only about 12% of all the energy released in the lamp filament by electric current is converted into light energy. Finally, the heat source of light is a flame. Grains of soot (fuel particles that did not have time to burn) are heated by the energy released during the combustion of fuel and emit light. Types of radiation
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Electroluminescence The energy required for atoms to emit light can also be obtained from non-thermal sources. In a discharge in gases, the electric field imparts large kinetic energy to the electrons. Fast electrons experience inelastic collisions with atoms. Part of the kinetic energy of electrons goes to excite atoms. Excited atoms release energy in the form of light waves. Due to this, the discharge in the gas is accompanied by a glow. This is electroluminescence. The Northern Lights are a manifestation of electroluminescence. The streams of charged particles emitted by the Sun are captured by the Earth's magnetic field. They excite the atoms of the upper layers of the atmosphere at the magnetic poles of the Earth, due to which these layers glow. Electroluminescence is used in advertising tubes. Types of radiation
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Chemiluminescence In some chemical reactions that release energy, some of this energy is directly spent on the emission of light. The light source remains cold (it has a temperature environment). This phenomenon is called chemiluminescence. In summer, you can see a firefly insect in the forest at night. He has a small green "flashlight" on his body. You won't burn your fingers by catching a firefly. The luminous speck on its back has almost the same temperature as the surrounding air. Other living organisms also have the ability to glow: bacteria, insects, many fish living at great depths. Pieces of rotting wood often glow in the dark. Types of radiation Contents
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Photoluminescence Light incident on a substance is partially reflected and partially absorbed. The energy of the absorbed light in most cases only causes heating of bodies. However, some bodies themselves begin to glow directly under the influence of the radiation incident on it. This is photoluminescence. Light excites the atoms of the substance (increases their internal energy), and after that they light up themselves. For example, luminous paints, which cover many Christmas decorations emit light after being irradiated. The light emitted by photoluminescence has, as a rule, a longer wavelength than the light that excites luminescence. This can be observed experimentally. If you direct a light beam passed through a violet light filter to a vessel with fluorescein (organic dye), then this liquid begins to glow with a green-yellow light, that is, light of a longer wavelength than that of violet light. The phenomenon of photoluminescence is widely used in fluorescent lamps. The Soviet physicist SI Vavilov proposed covering the inner surface of the discharge tube with substances capable of glowing brightly under the action of short-wavelength radiation from a gas discharge. Fluorescent lamps are about three to four times more economical than conventional incandescent lamps. Content
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Light sources The light source must consume energy. Light is electromagnetic waves with a wavelength of 4 × 10-7-8 × 10-7 m. Electromagnetic waves are emitted during the accelerated motion of charged particles. These charged particles are part of the atoms that make up matter. But, without knowing how the atom is structured, nothing reliable can be said about the mechanism of radiation. It is only clear that there is no light inside the atom, just as there is no sound in the piano string. Like a string that begins to sound only after the hammer is struck, atoms give birth to light only after they are excited. In order for an atom to begin to radiate, it needs to transfer a certain energy. Radiating, the atom loses the received energy, and for the continuous glow of the substance, an inflow of energy to its atoms from the outside is necessary. Content
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Spectral devices Simple devices such as a narrow slit limiting the light beam and a prism are no longer sufficient to accurately study spectra. Devices are needed that give a clear spectrum, that is, devices that separate waves of different wavelengths well and do not allow (or almost do not allow) the overlap of individual parts of the spectrum. Such devices are called spectral devices. Most often, the main part of the spectral apparatus is a prism or a diffraction grating. Let's consider the diagram of the device of the prism spectral apparatus (Fig. 46). The investigated radiation first enters a part of the instrument called a collimator. The collimator is a tube, at one end of which there is a screen with a narrow slit, and at the other end there is a collecting lens L1. Content
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The gap is on focal length from the lens. Therefore, the diverging light beam falling on the lens from the slit leaves it in a parallel beam and falls on the prism P. Since different refractive indices correspond to different frequencies, parallel beams emerge from the prism that do not coincide in direction. They fall onto the L2 lens. At the focal length of this lens is a screen - frosted glass or photographic plate. Lens L2 focuses parallel beams of rays on the screen, and instead of a single slit image, a whole series of images is obtained. Each frequency (more precisely, a narrow spectral interval) has its own image. All these images together form a spectrum. The described device is called a spectrograph. If instead of the second lens and screen, a telescope is used to visually observe the spectra, then the device is called a spectroscope. Prisms and other parts of spectral instruments are not necessarily made of glass. Instead of glass, transparent materials such as quartz, rock salt, etc. are also used. Contents
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Spectra According to the nature of the distribution of values of a physical quantity, spectra can be discrete (line), continuous (solid), and also represent a combination (overlay) of discrete and continuous spectra. Examples of line spectra are mass spectra and spectra of bound-bound electronic transitions of an atom; examples of continuous spectra are the spectrum of electromagnetic radiation of a heated solid and the spectrum of free electronic transitions of an atom; examples of combined spectra are the emission spectra of stars, where chromospheric absorption lines or most of the sound spectra are superimposed on the continuous spectrum of the photosphere. Another criterion for typing spectra is the physical processes underlying their acquisition. So, according to the type of interaction of radiation with matter, spectra are divided into emission (radiation spectra), adsorption (absorption spectra) and scattering spectra. Content
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Continuous Spectra The solar or arc-lamp spectrum is continuous. This means that all wavelengths are represented in the spectrum. There are no discontinuities in the spectrum, and on the spectrograph screen you can see a continuous multi-colored stripe (Fig. V, 1). Rice. V Emission spectra: 1 - continuous; 2 - sodium; 3 - hydrogen; 4 -helium. Absorption spectra: 5 - solar; 6 - sodium; 7 - hydrogen; 8 - helium. Content
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The frequency distribution of energy, that is, the spectral density of the radiation intensity, is different for different bodies. For example, a body with a very black surface emits electromagnetic waves of all frequencies, but the dependence of the spectral density of radiation intensity on frequency has a maximum at a certain frequency nmax. The radiation energy at very low and very high frequencies is negligible. As the temperature rises, the maximum of the spectral radiation density shifts towards short waves. Continuous (or continuous) spectra, as experience shows, give bodies in a solid or liquid state, as well as highly compressed gases. To obtain a continuous spectrum, the body must be heated to a high temperature. The nature of the continuous spectrum and the very fact of its existence are determined not only by the properties of individual emitting atoms, but also strongly depend on the interaction of atoms with each other. High-temperature plasma also gives a continuous spectrum. Electromagnetic waves are emitted by plasma mainly when electrons collide with ions. Types of spectra Contents
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Line Spectra Into the Pale Flame gas burner a piece of asbestos moistened with a solution of ordinary table salt. When observing a flame through a spectroscope, a bright yellow line flashes against the background of a barely discernible continuous spectrum of the flame. This yellow line is produced by sodium vapor, which is formed when table salt molecules break down in a flame. The figure also shows the spectra of hydrogen and helium. Each of them is a palisade of colored lines of varying brightness, separated by wide dark stripes. Such spectra are called line spectra. The presence of a line spectrum means that a substance emits light only at very specific wavelengths (more precisely, in certain very narrow spectral intervals). In the figure you can see the approximate distribution of the spectral density of the radiation intensity in the line spectrum. Each line has a finite width. Content
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Line spectra show all substances in a gaseous atomic (but not molecular) state. In this case, atoms emit light, which practically do not interact with each other. This is the most fundamental, basic type of spectra. Isolated atoms emit strictly defined wavelengths. Usually, to observe line spectra, the glow of a substance vapor in a flame or the glow of a gas discharge in a tube filled with a test gas is used. With an increase in the density of an atomic gas, individual spectral lines broaden, and, finally, with a very large compression of the gas, when the interaction of atoms becomes significant, these lines overlap each other, forming a continuous spectrum. Types of spectra Contents
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Striped Spectra The striped spectrum consists of individual bands separated by dark spaces. With a very good spectral apparatus, it can be found that each band is a collection of a large number of very closely spaced lines. Unlike line spectra, stripe spectra are not created by atoms, but by molecules that are not bound or weakly bound to each other. To observe molecular spectra, as well as to observe line spectra, the glow of vapor in a flame or the glow of a gas discharge is usually used. Types of spectra Contents
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Absorption spectra All substances whose atoms are in an excited state emit light waves, the energy of which is distributed in a certain way over wavelengths. The absorption of light by a substance also depends on the wavelength. So, red glass transmits waves corresponding to red light (l »8 × 10-5 cm), and absorbs all the rest. If white light is passed through a cold, non-emitting gas, then dark lines appear against the background of the continuous spectrum of the source. A gas absorbs most intensively the light of precisely those wavelengths that it emits in a highly heated state. The dark lines against the background of the continuous spectrum are absorption lines that together form an absorption spectrum. Types of spectra Contents
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Spectral analysis Line spectra play especially important role because their structure is directly related to the structure of the atom. After all, these spectra are created by atoms that do not experience external influences. Therefore, getting acquainted with the line spectra, we thereby take the first step towards studying the structure of atoms. By observing these spectra, scientists were able to "look" inside the atom. Here the optics are in close contact with atomic physics... The main property of line spectra is that the wavelengths (or frequencies) of the line spectrum of any substance depend only on the properties of the atoms of this substance, but do not depend at all on the method of excitation of the glow of the atoms. The atoms of any chemical element give a spectrum that is not similar to the spectra of all other elements: they are capable of emitting a strictly defined set of wavelengths. Spectral analysis is based on this - a method for determining the chemical composition of a substance by its spectrum. Like human fingerprints, line spectra have a unique personality. The uniqueness of the patterns on the skin of the finger often helps to find the culprit. In the same way, thanks to the individuality of the spectra, it is possible to determine chemical composition body. With the help of spectral analysis, it is possible to detect this element in the composition of a complex substance, even if its mass does not exceed 10-10 g. This is a very sensitive method. Presentation Content
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Spectra. spectral analysis. Spectral apparatus
Mantseva Vera
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Sources of radiation
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Types of spectra
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Continuous spectrum
These are spectra containing all wavelengths of a specific range. They emit heated solids and liquids, gases heated under high pressure. They are the same for different substances, so they cannot be used to determine the composition of a substance
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Line spectrum
Consists of separate lines of different or the same color, having different locations Emitted by gases, vapors of low density in the atomic state Allows you to judge the chemical composition of the light source by spectral lines
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Striped spectrum
Consists of a large number of closely spaced lines Produce substances in a molecular state
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Absorption spectra
This is a set of frequencies absorbed by a given substance. A substance absorbs those lines of the spectrum that it emits as a source of light Absorption spectra are obtained by transmitting light from a source giving a continuous spectrum through a substance whose atoms are in an unexcited state
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Meteor spectrum
It is almost impossible to aim a very large telescope at a short flash of a meteor in the sky. But on May 12, 2002, astronomers were lucky - a bright meteor accidentally flew just where the narrow slit of the spectrograph at the Paranal observatory was directed. At this time, the spectrograph was studying light.
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Spectral analysis
The method for determining the qualitative and quantitative composition of a substance by its spectrum is called spectral analysis. Spectral analysis is widely used in prospecting for minerals to determine the chemical composition of ore samples. It is used to control the composition of alloys in the metallurgical industry. On its basis, the chemical composition of stars was determined, etc.
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Spectroscope
To obtain a spectrum of radiation in the visible range, an instrument called a spectroscope is used, in which the human eye serves as a radiation detector.
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Spectroscope device
In the spectroscope, the light from the investigated source 1 is directed to the slit 2 of the tube 3, called the collimator tube. The slit gives off a narrow beam of light. At the second end of the collimator tube there is a lens that converts the diverging light beam into a parallel one. A parallel beam of light emerging from a collimator tube falls on the edge of a glass prism 4. Since the refractive index of light in glass depends on the wavelength, therefore, a parallel beam of light, consisting of waves of different wavelengths, is decomposed into parallel beams of light of different colors traveling along different directions... The telescope lens 5 focuses each of the parallel beams and gives an image of the slit in each color. Multi-colored images of the slit form a multi-colored stripe - a spectrum.
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TYPES OF SPECTROMETERS
Emission spectrometer for the analysis of lead and aluminum alloys.
Laser spark spectrometer (LIS-1)
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The spectrum can be observed through an eyepiece used as a magnifying glass. If you want to get a photograph of the spectrum, then the photographic film or photographic plate is placed in the place where the actual image of the spectrum is obtained. An instrument for photographing spectra is called a spectrograph.
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New NIFS Spectrograph Prepares for Shipment to Gemini North Observatory
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Types of spectrographs
High-resolution spectrograph NSI-800GS
Medium Power Spectrograph / Monochromator
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HARPS Spectrograph
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Spectral sensitivity of the human eye
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5. Choose one correct answer from the proposed options
What body radiation is thermal? Fluorescent light Incandescent light Infrared laser TV screen
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1. Choose one correct answer from the following options:
The researcher saw different spectra in four observations using an optical spectroscope. Which of the spectra is the thermal radiation spectrum?
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2. Choose one correct answer from the proposed options
only nitrogen (N) and potassium (K) only magnesium (Mg) and nitrogen (N) nitrogen (N), magnesium (Mg) and other unknown substance magnesium (Mg), potassium (K) and nitrogen (N)
The figure shows the absorption spectrum of an unknown gas and the absorption spectra of vapors of known metals. By analyzing the spectra, it can be argued that the unknown gas contains atoms
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3. Choose one correct answer from the proposed options
What bodies are characterized by striped absorption and emission spectra? For heated solids For heated liquids For rarefied molecular gases For heated atomic gases For any of the above bodies
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4. Choose one correct answer from the proposed options
hydrogen (H), helium (He) and sodium (Na) only sodium (Na) and hydrogen (H) only sodium (Na) and helium (He) only hydrogen (H) and helium (He)
The figure shows the absorption spectrum of an unknown gas and the absorption spectra of atoms of known gases. By analyzing the spectra, it can be argued that the unknown gas contains atoms:
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What bodies are characterized by line absorption and emission spectra? For heated solids For heated liquids For rarefied molecular gases For heated atomic gases For any of the above bodies
Continuous spectra give bodies in a solid, liquid state, as well as highly compressed gases. Line spectra show all substances in the gaseous atomic state. Isolated atoms emit strictly defined wavelengths. Band spectra, in contrast to line spectra, are not created by atoms, but by molecules that are not bound or weakly bound to each other.
They give bodies in a solid, liquid state, as well as dense gases. To get it, you need to heat the body to a high temperature. The nature of the spectrum depends not only on the properties of individual emitting atoms, but also on the interaction of atoms with each other. The spectrum contains waves of all lengths and there are no breaks. A continuous spectrum of colors can be observed on a diffraction grating. A good demonstration of the spectrum is the natural phenomenon of the rainbow. Uchim.net
All substances are given in a gaseous atomic (but not molecular) state (atoms practically do not interact with each other). Isolated atoms of a given chemical element emit waves of a strictly defined wavelength. For observation, use is made of the glow of a substance vapor in a flame or the glow of a gas discharge in a tube filled with the test gas. With an increase in the density of the atomic gas, individual spectral lines broaden. Uchim.net
The spectrum consists of individual bands separated by dark gaps. Each lane is a collection of a large number of very closely spaced lines. Created by molecules that are not bound or loosely bound to each other. For observation, use is made of the glow of vapors in a flame or the glow of a gas discharge. Uchim.net
Gustav Robert Kirchhoff Robert Wilhelm Bunsen Uchim.net Spectral analysis is a method for determining the chemical composition of a substance by its spectrum. Developed in 1859 by German scientists G.R. Kirchhoff and R.V. Bunsen.
If white light is passed through a cold, non-emitting gas, dark lines will appear against the background of the continuous spectrum of the source. A gas absorbs most intensively the light of the wavelengths that it emits in a highly heated state. The dark lines against the background of the continuous spectrum are absorption lines that together form an absorption spectrum. Uchim.net
New elements are discovered: rubidium, cesium, etc. Learned the chemical composition of the Sun and stars; Determine the chemical composition of ores and minerals; A method for controlling the composition of a substance in metallurgy, mechanical engineering, and the nuclear industry. The composition of complex mixtures is analyzed by their molecular spectra. Uchim.net
The spectra of the stars are their passports describing all the stellar features. Stars are composed of the same chemical elements that are known on Earth, but in percentage terms, they are dominated by light elements: hydrogen and helium. By the spectrum of a star, you can find out its luminosity, distance to the star, temperature, size, chemical composition of its atmosphere, rotation speed around its axis, features of movement around a common center of gravity. A spectral apparatus mounted on a telescope spreads the star's light along wavelengths into a strip of the spectrum. From the spectrum, you can find out what energy comes from a star at different wavelengths and estimate its temperature very accurately.
Stationary - spark optical - emission spectrometers "METALSKAN - 2500". Designed for accurate analysis of metals and alloys, including non-ferrous, ferrous alloys and cast iron. Laboratory electrolysis installation for the analysis of metals "ELAM". The installation is intended for carrying out a weight electrolytic analysis of copper, lead, cobalt and other metals in alloys and pure metals. Currently, television spectral systems (TSS) are widely used in forensics. - detection of various kinds of forgeries of documents: - detection of flooded, crossed out or faded (faded) texts, records formed by indented strokes or made on carbon paper, etc .; - identification of tissue structure; - detection of contamination on fabrics (soot and residues of mineral oils) in case of gunshot injuries and traffic accidents; - identification of washed out, as well as located on variegated, dark and contaminated objects of blood traces.
Spectra. spectral analysis. Spectral apparatus Sources of radiation Types of spectra
Emission spectra
- solid
- ruled
- striped
Absorption spectra
Continuous spectrum
- These are spectra containing all wavelengths of a specific range.
- They emit heated solids and liquids, gases heated under high pressure.
- They are the same for different substances, so they cannot be used to determine the composition of a substance
- Consists of separate lines of different or the same color, having different locations
- Emitted by gases, vapors of low density in the atomic state
- Allows you to judge the chemical composition of the light source by spectral lines
- Consists of a large number of closely spaced lines
- Gives substances that are in a molecular state
- This is a set of frequencies absorbed by a given substance. The substance absorbs those lines of the spectrum, which it emits, being a source of light
- Absorption spectra are obtained by transmitting light from a source giving a continuous spectrum through a substance whose atoms are in an unexcited state
- The method for determining the qualitative and quantitative composition of a substance by its spectrum is called spectral analysis. Spectral analysis is widely used in prospecting for minerals to determine the chemical composition of ore samples. It is used to control the composition of alloys in the metallurgical industry. On its basis, the chemical composition of stars was determined, etc.
- To obtain a spectrum of radiation in the visible range, a device called spectroscope in which the human eye serves as a radiation detector.
2. Choose one correct answer from the options offered only nitrogen (N) and potassium (K) only magnesium (Mg) and nitrogen (N) nitrogen (N), magnesium (Mg) and another unknown substance magnesium (Mg), potassium (K ) and nitrogen (N)
The figure shows the absorption spectrum of an unknown gas and the absorption spectra of vapors of known metals. By analyzing the spectra, it can be argued that the unknown gas contains atoms
3. Choose one correct answer from the options offered What bodies are characterized by striped absorption and emission spectra? For heated solids For heated liquids For rarefied molecular gases For heated atomic gases For any of the above bodies
4. Choose one correct answer from the options offered What bodies are characterized by line absorption and emission spectra? For heated solids For heated liquids For rarefied molecular gases For heated atomic gases For any of the above bodies
5. Choose one correct answer from the proposed options. Which body radiation is thermal? Fluorescent light Incandescent light Infrared laser TV screen
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