Plan teoretical principles of ir- spectroscopy


НазваPlan teoretical principles of ir- spectroscopy
Дата конвертації30.04.2013
Розмір445 b.
ТипПрезентации



PLAN

  • Teoretical principles of IR- spectroscopy.

  • Connection oscillation spectrums with the structure of organic compounds.

  • Devices for IR-spectroscopy: basic knots, basic scheme and purpose.

  • Methods of recording the spectrums in the method of infrared spectroscopy.

  • Qualitative and quantitative analysis of infrared spectroscopy.

  • Spectroscopy of SR (raman spectroscopy)



1.Teoretical principles of IR- spectroscopy

  • IR-spectroscopy is an optical method of analysis, which is based on measuring absorption of radiation spectrum of IR- area (200-300 сm-1 – 4000-5000 сm-1)



1.Teoretical principles of IR- spectroscopy

  • Swaying transitions and proper to them the swaying spectrums of molecules can be got both at direct absorption by the substance of infrared (range of waves 2 - 50 mcm) and at absorption of visible and the ultraviolet radiation. In the last cases only part of eaten up energy is outlaid on excitation of molecules, greater part change by the substance. In accordance with it oscilation spectroscopy is divided into infra-red (IR) spectroscopy and spectroscopy of combination dispersion (CD).



Conditions receipt of IR-spectrums

  • That a molecule absorbs energy of IR-radiation, at vibrations must change its dipole moment. At cooperating of IR-radiation with the molecule oscilation component of field cooperates with the oscilation dipole moment of a molecule.



The frequency of oscillation transitions

  • A molecule is the mechanical system, for example, as a system of marbles which symbolize atoms, and springs which link them and they are symbolize contacts between atoms.



The frequency of oscillation transitions

  • By law of Guk the frequency of vibrations of such system:

  • where

  •  -frequency of vibrations;

  • C - speed of a light;

  • K - power permanent to connection;

  • m - resulted mass of the system that calculation through the masses of atoms by the formula



The levels of energy of the diatomic molecule



The energy in oscilation motions of molecules is quantized. It's a size for so urgent harmonic oscillator can be found from expression:

  • The energy in oscilation motions of molecules is quantized. It's a size for so urgent harmonic oscillator can be found from expression:

  • where

  • V - oscillation quantum number which takes on the value of natural numbers: 0, 1, 2

  •  - the frequency of basic oscillation



Most registered by a spectrometer stripes of absorption are conditioned by a transition Vо –> V1 –it is answered by fundamental frequency.

  • Most registered by a spectrometer stripes of absorption are conditioned by a transition Vо –> V1 –it is answered by fundamental frequency.

  • Transition Vо –> V2, named first overtone.

  • Transition Vо –> V3, named second overtone.

  • By the rules of selection the settled vibrations for which ∆V=1.

  • The frequency of overtones is more high of the fundamental frequency in 2 and 3 times accordingly. The intensity of overtones is less.



Normal vibrations - are the independent movements of a molecule, which repeat oneself in itself.

  • It is existed for the nonlinear molecule 3N-6 normal vibrations which predetermine the changing of lengths bonds in a molecule or corners between bonds.

  • It is existed for the linear molecule 3N-5 normal vibrations which predetermine the changing of lengths bonds in a molecule or corners between bonds.



Designation of the frequencies of main vibrations

  • 1, 2 , 3 - fullsymetric vibrations

  •  - valence vibrations

  • s – symmetric valence vibrations

  • as – asymmetric valence vibrations

  •  - deformation vibrations

  • π – outside spaces vibrations

  • d – degenerate valence vibrations



Valence oscillation is oscillation at which is changed of length bonds without the substantial changing of the valence angles.

  • Valence oscillation is oscillation at which is changed of length bonds without the substantial changing of the valence angles.

  • Deformation vibrations are oscillation in which are changed of valence angles.



2. Connection oscillation spectrums with the structure of organic compounds.

  • Conception of group vibrations: in the spectrum of difficult molecule can look after the stripes absorption of different functional groups or write stripes in a spectrum to different functional groups.



A molecule is divided into groups and oscillation of every group are added one or a few stripes in a spectrum.

  • Methyl group СН3- has 5 characteristic strips absorption :

  • 2 strip 3000-2860 as і s

  • 1 strip 1470-1400 as

  • 1 strip 1380-1200 s

  • 1 strip 1200-800  pendulum



!!! In difficult molecules there are many group vibrations which are recovered and taking of stripes in the spectrum becomes heavy.

  • Conception of grouping vibrations provides for, that vibrations of this group do not relatively depend on other part of molecule, that it is impossible, if the center mass remains on the previous place.



The valency oscillation of carbonic group =С=О in different molecules characterized by a stripe~ 1700 сm-1.

  • The valency oscillation of carbonic group =С=О in different molecules characterized by a stripe~ 1700 сm-1.

  • Position of this stripe can change 150 nm depending on the mass change group which added of carbonic group, depending on its inductive interface.



Summary of absorptions of bonds in organic molecules







Interpretation of IR-spectrums of polyatomic molecules

  • Carried out on the basis of studies about symmetry of molecules and theory of groups.

  • The mathematical vehicle of its studing allows to calculate the number of frequencies and rule of selection for molecules of different symmetry.





Spectrum of 1-Octene.



3. Devices for IR-spectroscopy: basic knots, basic scheme and purpose.



  • Basic knots of device:

  • The source of radiant: shtift of Nernsta and globar.

  • Monochromatizatories: prisms from LiF, NaCl, KBr .

  • Cuvettes: the same material as for monochromatizatories.

  • The receiver of light: photoelements, themoelements and ballometers.





4. Methods of recording the spectrums in the method of infrared spectroscopy.









Recording spectrums of liquids or solid substances in solution



Recording spectrums of solid substances in a suspension with the vaselinic oil



Recording spectrums of solid substances in disks with potassium bromide



A device for retaining of disks



Recording spectrums of gaseous substances

  • The gaseous investigate standards in the special gas cuvettes is a cylinder about 10 cm with windows from KBr and CaF2 and by vacuum faucets for filling gas or its pumping.





5. The qualitative analysis in IR-spectroscopy is an area of finger-prints 1300 – 600 cm-1

  • identification by comparing the spectrums of investigated and standard samples;

  • identification with useing of standard spectrums.



Quantitative analysis in IR-spectroscopy



Quantitative analysis in IR-spectroscopy.



The possibilities of methods of oscillation spectroscopy



6. Spectroscopy of SR (raman spectroscopy)

  • Optical method of analysis, which are based on measuring of the intensity of dissipated radiation.

  • In the spectrum of SR active only those normal vibrations at which changing polarization of a molecule.

  • The spectrum of SR arises up at the irradiation substance of light UV or visible range.



Raman spectroscopy is a spectroscopic technique used to study vibrational, rotational, and other low-frequency modes in a system. It relies on inelastic scattering, or Raman scattering, of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range.

  • Raman spectroscopy is a spectroscopic technique used to study vibrational, rotational, and other low-frequency modes in a system. It relies on inelastic scattering, or Raman scattering, of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range.

  • For a vibration to be Raman active, the polarizability of the molecule must change with the vibrational motion. Thus, Raman spectroscopy complements IR spectroscopy.



The rising of spectrum of SR

  • Under the action of monochromatic light stream with frequency  the molecules of substance are polarized and disperse light with frequency  (rayleigh dispersion), and also with frequencies  ± 0і ,

  • where 0і – frequency of normal vibrations of a molecule.



The rising of spectrum of SR

  • Oscillations frequencies are observed as petticoat displacements of frequency of excitant light in the ultraviolet or visible area of a spectrum.

  •  - rayleigh frequency

  •  - 0і - stoces frequency

  •  +0і - antistoces frequency



h + E′ = hr + E″





In molecular compounds are often possible to associate the different Raman peaks with the characteristic vibrational modes of interatomic bonds or functional groups (d = bending, n = stretching).

  • In molecular compounds are often possible to associate the different Raman peaks with the characteristic vibrational modes of interatomic bonds or functional groups (d = bending, n = stretching).



Application of raman spectroscopy

  • Application of raman spectroscopy

  • Raman spectroscopy is commonly used in chemistry, since vibrational information is specific to the chemical bonds and symmetry of molecules. It therefore provides a fingerprint by which the molecule can be identified. For instance, the vibrational frequencies of SiO, Si2O2, and Si3O3 were identified and assigned on the basis of normal coordinate analyses using infrared and Raman spectra.

  • Another way that the technique is used is to study changes in chemical bonding, e.g., when a substrate is added to an enzyme.

  • Raman gas analyzers have many practical applications. For instance, they are used in medicine for real-time monitoring of anaesthetic and respiratory gas mixtures during surgery.





Схожі:

Plan teoretical principles of ir- spectroscopy iconTime scale principles Time scale principles

Plan teoretical principles of ir- spectroscopy iconPlan: Early history

Plan teoretical principles of ir- spectroscopy iconPlan Industrialization of Ukraine

Plan teoretical principles of ir- spectroscopy iconPlan: Early history

Plan teoretical principles of ir- spectroscopy iconInternational Bureau of Credit Histories Principles of work


Додайте кнопку на своєму сайті:
dok.znaimo.com.ua


База даних захищена авторським правом ©dok.znaimo.com.ua 2013
звернутися до адміністрації
dok.znaimo.com.ua
Головна сторінка