Molecular physics

Branch of Physics

Molecular physics (molecular physics) is a research molecular structure , molecule physical property and Intermolecular interaction Of Branch of Physics 。 from microcosmic From the perspective of molecule Geometry of structure And molecular energy level Structure, interaction between molecules, which is an important part of material structure research; from macroscopic From the perspective of molecule Constituent system Followed motion Laws, this part is called Molecular kinetic theory 。 On the basis of the above theoretical research Gas 、 liquid and solid Of Physicochemical Properties are also the main content of molecular physics. It is related to physics Other branches of, such as Atomic physics 、 Condensed matter physics 、 Astrophysics Etc. and Chemistry Are closely related relationship 。^[1]

Chinese name: Molecular physics
Foreign name: molecular physics

Applicable fields: Condensed matter physics
Discipline: Astrophysics
Main theories: Molecular kinetic theory, molecular thermodynamics, etc.

catalog

▪ Experimental methods
▪ Theoretical interpretation and calculation
three Development and application

four Related branch disciplines

brief history

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Molecular kinetic theory Its development can be traced back to the 17th century. 1650 R Boyle Studied gas state And outside The relationship between conditions later developed into ideal gas Of state equation 。 18th century D Bernoulli Gives Molecular motion And pressure The relationship between, and Russia Scientist M Romonosov Explain all kinds of phenomenon , developed molecules thermodynamics The two of them are believed to be based on the theory of molecular motion founder 。 nineteenth century J. maxwell And L Boltzmann Studied gas Molecular motion Of velocity distribution The famous Maxwell Boltzmann distribution Laws 。 Later, it developed on the basis of molecular motion theory thermodynamics and statistical mechanics , the microscopic movement of molecules and Interaction Macroscopic composition with a large number of molecules material Of physical property Connect. Twentieth Century The viewpoint of molecular kinetic theory is used to study chemical reaction Of rate and mechanism , promoted chemical kinetics Development of. The development of micro molecular physics is based on atomic physics and quantum mechanics Establishment of, experiment Pass on Molecular spectrum and Electromagnetic spectrum Of determination To understand the molecular energy level Structure and geometry Structure. In this regard G Herzberg He has made outstanding contributions and is recognized as“ Molecular spectrum Father, 1971 Nobel Prize in Chemistry 。 His four volumes of Molecular Spectra and Molecular Structure are about molecular physics and molecules spectroscopy Important literature.^[1]

Contents and methods

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executive summary

Molecules are atom Composed of atoms through chemical affinity or Chemical bond The geometric structure and chemical bond of molecules are directly related to the chemical and physical properties of molecules. Molecular structure It can be studied in many ways Spectral measurement The method is research molecular structure Important and effective means. adopt Molecular spectrum Of measure Molecular microcosmic Energy level structure, and then give the geometric structure of molecules and intermolecular Interaction force 。 Compared with atoms, the internal motion of molecules is much more complex, except that they have the same periphery as atoms Electronics In addition to the movement around the nucleus Nucleus Inter Vibration And all the nuclei around the molecular axis turn , which determines that the microscopic energy level structure of the molecule is more complex than that of the atom, so the molecular spectrum is also quite complex. Molecular spectroscopic wavelength The measurement range can cover from ultraviolet rays reach microwave 、 radio frequency The molecular spectra of different wavebands represent different energy level Inter transition ： visible light And UV band spectrum It reflects the transition between the energy levels of the molecular electronic states and forms the structure of the spectral band system; The infrared spectrum reflects the transition between the molecular vibrational dynamic energy levels; The far infrared to microwave band reflects the transition between molecular rotational energy levels.^[1]

Experimental methods

Molecular spectrum measurement can adopt various Spectral instrument , such as Grating spectrometer or Spectrograph 、 Fourier Spectrometer Raman spectrometer Etc. laser After its launch Laser spectrum Measurement technology, combined molecular beam Technology mass spectrum Technology becomes important in molecular spectrum research means 。 The measurement of molecular spectrum can be divided into two categories: one is frequency domain measurement, that is, measurement spectrum strength Follow the light frequency (or light wavelength ）Change relationship of; One is time domain measurement, that is, measuring spectral intensity versus time Change relationship of. Frequency domain measurement can give molecular Spectral constant And energy levels parameter , molecular potential energy Functional, molecular Dissociation energy , intermolecular Force constant And derive the molecular geometry (such as Bond angle and Key length ）。 high resolution Molecular spectrum The measurement of can give the molecular fine structure and Hyperfine structure 、 Nuclear spin Parameters, can also be used to study the molecular electric field And outside magnetic field In behavior , giving the molecular electromagnetism Parameters (such as molecular Magnetic dipole moment and Electric dipole moment , electric quadrupole moment and Polarizability Etc.). Time domain measurement is widely used to study ultrafast in molecular physics phenomenon , using ultrashort pulse Laser measurable excited state Molecules and transient Molecular life , measure the molecular light dissociation and chemical reaction In process dynamics Behavior, revealed in picosecond 、 femtosecond Internal movement of matter in the field law 。 except spectrum Outside the study, X-ray diffractometer Neutron Diffractometer 、 Nuclear magnetic resonance spectrum Instrument and Electron paramagnetic resonance spectrometer It can also be used to determine the molecular structure. In addition, photoelectron Energy spectrum measurement technology is also used to study molecules physical property The power of Experimental means 。^[1]

Theoretical interpretation and calculation

theory upper quantum mechanics Is research Molecular physics , molecule Chemical bond Essence and Intermolecular interaction The main tool of. Since 1930, the theory of quantum mechanics in these problems explain Great progress has been made. Known as the quantum mechanics of molecules quantum chemistry , modern times Theoretical chemistry One of the most active frontier research. Apply the principles of quantum chemistry and cooperate computer technology , direct calculation Energy level and state of molecule wave function and potential function , and other physical properties. Conversely, molecules Spectral measurement Is consistent with the interpretation of quantum mechanics confirm The important basis of quantum theory.

Theory of molecular motion It studies a large number of molecules macroscopic Movement rules, such as ideal gas Motion rules, molecules velocity distribution Laws and kinetic energy The law of equipartition, etc heat Nature and aggregation state state equation （ volume 、 temperature and pressure Relationship), various Thermodynamic function , liquid and solid Surface layer Phenomena and Surface adsorption 、 phase equilibrium and phase transition , and spread 、 heat conduction and Viscosity Equal and molecule Transport Related phenomena. These phenomena and properties are related to the whole It is also widely used in the research of molecular physics Thermodynamic law and Statistical Physics The theory of.^[1]

Development and application

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The molecule is material Can retain chemistry attribute Minimum of unit The research of molecular physics has a strong interdisciplinary characteristic astronomy 、 environmental science 、 life sciences and material science Are closely linked. In the field of chemical research, the understanding of chemical reaction has developed from macroscopic phenomenon to microscopic mechanism, and the process of chemical reaction is understood based on the molecular level. Important achievements in this regard include: D Herschbach and Li Yuanzhe utilize Cross molecular beam technique And J Polani Using infrared chemiluminescence technology to study chemical reaction kinetics Nobel Prize in Chemistry ； Ahmed Zewell Created femtosecond Laser spectrum The method of studying chemical reaction was awarded in 1999 Nobel Prize in Chemistry 。 The research results of molecular physics and molecular spectroscopy give chemical reaction dynamics and photochemistry Process research provides important parameters and scientific basis. On the contrary, the free radical molecules appearing in the middle process of chemical reaction are the focus of molecular physics and molecular spectroscopy object 。 People try to select molecules with specific energy states for chemical reaction, and have a deep understanding of intermolecular collision and energy transfer Process until the molecular Design and Clipping 。 Astronomy and molecular physics are also closely linked. Many important free radical molecules and ionic molecules were originally created by Astronomical observation Discovered; The research of molecular physics provides accurate measurement for astronomical observation parameter , these studies human beings explore universe Evolution and Origin of life Both play an important role. stay life sciences and material science In the research field, many studies have entered the molecular level, such as biological research molecular structure Research Biomolecule Inter energy and information transfer Process research Functional polymer materials The research of relevant 。^[1]

Related branch disciplines

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Molecular physics Sub discipline: quantum mechanics Nuclear physics 、 high-energy physics 、 Atomic physics 、 Condensed matter physics 、 Astrophysics , mechanics, heat, optics acoustics Electromagnetics, solid state physics.

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