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UV VISIBLE SPECTROSCOPY

1. UV-Visible Spectroscopy Ankita Parmanik

2. Spectroscopy Principle of spectroscopy Absorption and emission spectroscopy Electromagnetic radiation Properties of EMR Wavelength and frequency

3. The word spectroscopy is derived from spectrum which means a band of different colours formed due to difference in wavelength and its examination or evaluation. Thus, spectroscopy is the branch of science that deals with the examination or evaluation of spectrum. It is defined as the interaction between the matter & EMR. It deals with emission as well as absorption spectra. It is used to measure the energy difference between various molecular energy levels & to determine the atomic & molecular structures. The instruments used in such studies are called spectrophotometer. Spectroscopy

4. Spectroscopy Spectroscopy is the branch of science dealing the study of interaction of electromagnetic radiation with matter The principle is based on the measurement of spectrum of a sample containing atoms.  Spectrum is a graph of intensity of absorbed or emitted radiation by sample verses frequency (V) or wavelength (λ).  Spectrometer is an instrument design to measure the Spectrum of a compound Absorption Spectroscopy :- An analytical technique which concerns with the measurement of absorption of electromagnetic radiation. E. g : UV (185-400nm) / Visible (400-800nm) spectroscopy. IR Spectroscopy (0.76-15 μ m). Emission Spectroscopy :- An analytical technique which emission of a particle or radiation is dispersed according to some property of the emission & the amount of dispersion is measured eg . Mass spectroscopy. Electromagnetic Radiation:- Electromagnetic radiation consist of discrete packets of energy which called as photons . A photons consists of an oscillating electric field (E) & An oscillating magnetic field (M) which are perpendicular to each other

5. Terms of electromagnetic radiation 1) Wavelength :- it is distance b/w two successive maxima on an electromagnetic wave. Unit are m,cm,mm,nm and micrometer. 2) Frequency:- Number of wavelength units pass time is called as frequency. It is denoted by “V” and units are cycle per sec. Hertz. 3) Wavenumber 𝒗=𝟏𝒘𝒂𝒗𝒆𝒍𝒆𝒏𝒈𝒕𝒉 As the number of waves per cm in vaccum

6. Electronic Transition:- 1) σ → σ * transition:  The energy required is large.  For exp. Methane (which has only C-H bonds and can only undergo σ → σ * transition Transition) shows an absorbance maximum at 125nm.  Absorption maxima due to σ →σ transition are not seen in typical UV-Vis Spectra (200-700nm) but in UV- region (125-135nm). 2) n→ σ * Transition:-  These transition Usually need less energy then n→σ * transition.  They can be initiated by light whose wavelength is in the range 150-250nm.  The number of organic functional groups with n →σ* peaks in the UV region in small. 3) π →π* Transition:-  Π electron in a bonding orbital is exaited to corresponding antibonding orbital π* and obserbed in conjugated compounds  Eg . Alkenes generally absorb in the regin 170 to 205 nm. 4) n→ π* transition:-  n→π9 transition require minimum energy and show absorption at longer wavelength around 300nm.

7. Terms Used In UV/Visible Spectroscopy Chromophore :- The part of a molecule responsible for imparting color are called as chromospheres. The functional group comtaining multiple bonds capable of absorbing radiations above 200nm due to n→π* & π→π* transitions eg. NO 2 , N=O, C=N, C≡N, C=C, C=S etc. Auxochrome :- The functional group with non bonding electrons that dose not absorb radiation in near UV region but when attached to a chromophore alters the wavelength & intensity of absorption. Eg . Benzene λ max =255nm. Phenol λ max =270nm. Aniline λ max =280nm.

8. UV Visible Spectroscopy Theory involved : When a beam of light falls on a solution or homogenes media a surface of the media a portion is absorbed with in the medium and remaining is transmitted through the medium