Lecture 2

1. Lecture 2 Spectroscopy: theory, classification, application Assistant of the pharmaceutical chemistry department Burmas Nataliya Ivanivna e-mail: Natashenka-Burmas@rambler.ru

2. PLAN 1. Essence of spectroscopic methods of analysis. 2. The main characteristics of electromagnetic radiation. 3. Classification of spectroscopic methods of analysis. 4. Utilizing spectroscopy in analysis.

3. 1. Essence of spectroscopic methods of analysis. The spectroscopic methods of analysis are based on cooperating of the electromagnetic radiation with a substance.

5. 2. The main characteristics of electromagnetic radiation. The electromagnetic radiation is described based on: • the wave‘s nature of light (break of a light , scattering, diffraction, refraction of a light); • the corpuscular nature of a light (absorption and emanation of a light by meals - quantum).

6. Electromagnetic radiation (often abbreviated E-M radiation or EMR) is a phenomenon that takes the form of self-propagating waves in a vacuum or in a matter. It consists of electric and magnetic field components which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation.

7. The characteristic of electromagnetic radiation as a wave: a) the wave's length is a spatial period of a wave – the distance over which the wave's shape repeats; b) a frequencyis the number of occurrences of a repeating event per unit time; c) the waven'snumber is the number of wavelengths per unit distance, that is, 1/λ where λ=wavelength

9. The concept was expanded greatly to comprise any measurement of a quantity as a function of either wavelength or frequency. Thus it also can refer to a response to an alternating field or varying frequency (ν). A further extension of the scope of the definition added energy (E) as a variable, once the very close relationship E = hν for photons was realized (h is the Planck constant). • h = 6,6262·10-34J·s • с = 2,9979 ·108M·s-1

10. Electromagnetic spectrum Absorption energy occurs at the excitation elementary systems (nuclear, atomic, molecular) and move her to a lower energic level to a higher level.

11. Electromagnetic radiation is classified into several types according to the frequency of its wave; these types include (in order of increasing frequency and decreasing wavelength): • radio waves, • microwaves, • terahertz radiation, • infrared radiation, • visible light, • ultraviolet radiation, • X-rays • gamma rays.

12. A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object.

13. The spectrum of absorption

14. The intensity of the absorption varies as a function of frequency, and this variation is the absorption spectrum.

17. Types of spectrums: • radiation (emission spectroscopy) • absorption (absoption spectroscopy) • reflection (spectroscopy of reflection) • dispersion (IR spectroscopy) • luminescence (luminescent spectroscopy)

18. 3.Classification of spectroscopic methods of analysis. The type of spectroscopy depends on the physical quantity measured. Normally, the quantity that is measured is an intensity, either of energy absorbed or produced. I. Nature of excitation measured: • Electromagnetic spectroscopy involves interaction of matter with electromagnetic radiation, such as light. • Electron spectroscopy involves interactionwith electron beams. • Dielectric spectroscopy involves the frequency of an external electrical field. • Mechanical spectroscopy involves the frequency of an external mechanical stress, e.g. a torsion applied to a piece of material.

19. II. Along with that distinction, they can be classified on the nature of their interaction: • Absorption spectroscopy uses the range of the electromagnetic spectra in which a substance absorbs. • Emission spectroscopy uses the range of electromagnetic spectra in which a substance radiates (emits). The substance first must absorb energy. This energy can be from a variety of sources, which determines the name of the subsequent emission, like luminescence. • Scattering spectroscopy measures the amount of light that a substance scatters at certain wavelengths, incident angles, and polarization angles.

21. Rotational spectroscopy or microwave spectroscopy studies the absorption and emission of electromagnetic radiation (typically in the microwave region of the electromagnetic spectrum) by molecules associated with a corresponding change in the rotational quantum number of the molecule. The use of microwaves in spectroscopy essentially became possible due to the development of microwave technology for RADAR during World War II. Rotational spectroscopy is only really practical in the gas phase where the rotational motion is quantized. In solids or liquids the rotational motion is usually quenched due to collisions.

22. 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. The laser light interacts with phonons or other excitations in the system, resulting in the energy of the laser photons being shifted up or down. The shift in energy gives information about the phonon modes in the system.

23. Fluorescence spectroscopy is a type of electromagnetic spectroscopy which analyzes fluorescence from a sample. It involves using a beam of light, usually ultraviolet light, that excites the electrons in molecules of certain compounds and causes them to emit light of a lower energy, typically, but not necessarily, visible light. A complementary technique is absorption spectroscopy.

24. X-ray absorption spectroscopy (XAS) is a widely-used technique for determining the local geometric and/or electronic structure of matter. The experiment is usually performed at synchrotron radiation sources, which provide intense and tunable X-ray beams. Samples can be in the gas-phase, solution, or condensed matter (ie. solids).

25. 4. Utilizing spectroscopy in analysis Spectrums used both for qualitative analysis and also for quantitative analysis. The qualitative analysis is the position (energy, frequency, length of wave, wave‘s number) of maximums (lines) in the electromagnetic spectrum.

26. Quantitative analysis is anintensity (amplitude) of spectral line is the function of concentration substance. To use such description of spectral line, which straight proportional the concentration of a substance. • For example, optical density:

27. Spectroscopy/spectrometry is often used in physical and analytical chemistry for the identification of substances through the spectrum emitted from or absorbed by them. • Spectroscopy/spectrometry is also heavily used in astronomy and remote sensing. Most large telescopes have spectrometers, which are used either to measure the chemical composition and physical properties of astronomical objects or to measure their velocities from the Doppler shift of their spectral lines.

28. Spectroscopy is the use of the absorption, emission, or scattering of electromagnetic radiation by matter to qualitatively or quantitatively study the matter or to study physical processes. Absorption: A transition from a lower level to a higher level with transfer of energy from the radiation field to an absorber, atom, molecule, or solid. • Emission: A transition from a higher level to a lower level with transfer of energy from the emitter to the radiation field. If no radiation is emitted, the transition from higher to lower energy levels is called nonradiative decay. • Scattering: Redirection of light due to its interaction with matter. Scattering might or might not occur with a transfer of energy, i.e., the scattered radiation might or might not have a slightly different wavelength compared to the light incident on the sample.

29. Thank you for attention!