Applications and Prospects of Spectroscopy

Light waves are produced by electrons moving inside atoms. The movement of electrons inside the atoms of various substances is different, so they emit different light waves. The study of light-emitting and light-absorbing situations of different substances, which are important theoretical and practical significance, has become a specialized discipline - spectroscopy.

The emission spectrum of light-emitting objects directly produced by the spectrum is called the emission spectrum. The emission spectrum has two types: continuous spectrum and bright line spectrum.

A continuously distributed spectrum containing light of various colors from red to violet is called a continuous spectrum. The emission spectra of hot solids, liquids and gases under pressure are continuous spectra. For example, the light emitted by an electric filament and the light emitted by hot steel form a continuous spectrum.

A spectrum containing only a few discontinuous bright lines is called a bright-line spectrum. The bright lines in a bright-line spectrum are called spectral lines, and each line corresponds to a different wavelength of light. The emission spectrum of a dilute gas or a vapor of a metal is a bright-line spectrum. Bright-line spectra are emitted by atoms in their free state, so they are also called atomic spectra. To observe the atomic spectrum of a gas, you can use a spectrometer tube, which is a closed glass tube that is thin in the center and contains a low-pressure gas, with two electrodes at each end of the tube. The two electrodes are connected to a high-voltage power supply, and a glow discharge occurs in the thin gas in the tube, producing light of a certain color.

To observe the atomic spectra of solid or liquid substances, you can put them into the flame of a gas lamp or an electric arc to burn them, so that they gasify and then emit light, and then you can see their bright-line spectra from the spectroscope.

Experiments have proved that atoms are different and emit different bright-line spectra, and the atoms of each element have a certain bright-line spectrum. Each atom can only emit certain wavelengths of light with its own characteristics, therefore, the spectral lines of the bright-line spectrum are called the characteristic spectral lines of atoms. The characteristic spectral lines of atoms can be used to identify substances and to study the structure of atoms.

Absorption Spectrum White light emitted by a high-temperature object (which contains a continuous distribution of all wavelengths of light) passes through a substance, and certain wavelengths of light are absorbed by the substance to produce a spectrum, called the absorption spectrum. For example, if you let the white light from an arc lamp pass through sodium gas at a lower temperature (put some table salt on the core of an alcohol lamp, and sodium gas will be produced when the table salt is decomposed by heat), and then observe it with a spectroscope, you will see two dark lines close to each other in the background of the continuous spectrum, which is the absorption spectrum of sodium atoms. It is worth noting that each dark line in the absorption spectrum of various atoms corresponds to a bright line in the emission spectrum of that atom. This indicates that the light absorbed by a low-temperature gas atom happens to be the light emitted by such an atom at high temperatures. Therefore, the spectral lines (dark lines) in the absorption spectrum are also the characteristic spectral lines of the atom, except that fewer characteristic spectral lines are usually seen in the absorption spectrum than in the bright-line spectrum.

Spectral Analysis Since each atom has its own characteristic spectral line, it is possible to identify a substance and determine its chemical composition based on the spectrum, a method called spectral analysis. Spectral analysis can be done using either the emission spectrum or the absorption spectrum. The advantage of this method is that it is very sensitive and rapid. If an element is present in a substance in an amount of 10-10 grams, its characteristic spectral lines can be found in the spectrum and it can be detected. Spectral analysis has a wide range of applications in science and technology:

1. Spectral analysis is used when checking whether the semiconductor materials silicon and germanium are of high purity;

2. In history, spectral analysis has also helped people discover many new elements, e.g. rubidium and cesium were discovered by seeing previously unknown characteristic spectral lines in the spectra;

The spectrum is divided into the following forms

(1) Linear spectra.

A spectrum consisting of narrow spectral lines. Light waves emitted by monatomic gases or metallic vapors have line spectra, so line spectra are also called atomic spectra. When the atomic energy jumps from a higher energy level to a lower energy level, it radiates a light wave with a single wavelength. Strictly speaking, this wavelength of a single monochromatic light does not exist, due to the energy level itself having a certain width and the Doppler effect and other reasons, the atomic radiation of the spectral lines will always have a certain width (see spectral line broadening); that is, in the narrower range of wavelengths still contains a variety of different wavelengths of the components. Atomic spectra by wavelength distribution law reflect the internal structure of atoms, each atom has its special spectral series. Through the study of atomic spectra can understand the internal structure of atoms, or qualitative and quantitative analysis of the components contained in the sample.

(2) Band spectrum.

Consists of a series of spectral bands that are radiated by molecules, so it is also called the molecular spectrum. When observed with a high-resolution spectrometer, each band is composed of many spectral lines close together. The band spectra are radiated by molecules as they jump between their vibrational and rotational energy levels and are usually located in the infrared or far-infrared region. The study of molecular spectra provides insight into the structure of molecules.

(3) Continuous spectrum.

A spectrum that includes all wavelengths; the spectrum radiated by a red-hot solid is continuous. Sources of synchrotron radiation (see electromagnetic radiation) can emit a continuous spectrum from microwaves to X-rays, and the bremsstrahlung portion of the spectrum emitted by X-ray tubes is also continuous.

(4) Absorption spectrum.

When a light wave with a continuous spectrum passes through a material sample, the atoms or molecules in the ground state of the sample will absorb the light of a specific wavelength and jump to the excited state, so the corresponding dark lines or dark bands appear on the background of the continuous spectrum, known as the absorption spectrum. Each kind of atom or molecule has its energy level structure to reflect the identity of the absorption spectrum. The study of the characteristics and laws of absorption spectra is an important means of understanding the internal structure of atoms and molecules. Absorption spectra were first discovered by J. V. Fraunhofer and Fay in the solar spectrum (called Fraunhofer and Fay lines) and were used to identify certain elements contained in the sun. Specific elemental spectra: red for sulfur, blue for oxygen, and green for hydrogen.

Spectroscopy Instruments Continue to Broaden Applications

Future spectroscopic instruments will still be along the end of the last century has begun to broaden the application surface, the transfer of the direction of development will be by the traditional scientific and technological basic disciplines (science, chemistry, astronomy, biology), mineral analysis, product quality control of industrial products and other theoretical research, the material production areas continue to biomedicine, environment and ecology, social security, national defense and other areas of direct relevance to the expansion of the human being.