Ultraviolet Molecular Spectroscopy

The interaction of UV and visible radiation with matter can provide qualitative identification of molecules and polyatomic species, including ions and complexes. Structural information about molecules and polyatomic species, especially organic molecules, can be acquired. This qualitative information is usually obtained by observing the UV /VIS spectrum, the absorption of UV and visible radiation as a function of wavelength by molecules. A typical UV absorption spectrum is shown in Fig. 5.1. The spectrum may be plotted as wavelength vs. absorbance, transmittance, or molar absorptivity, s. The molar absorptivity is defined subsequently. In Fig. 5.1, the absorption spectrum of pyridine dissolved in ethanol is plotted as log s vs. wavelength in angstroms (A). 

Quantitative information can also be obtained by studying the absorption or emission of UV and visible radiation by molecules or polyatomic species. As a very simple example, we can look at the absorption spectrum of a red solution such as red ink in water (Fig. 5.2). It can be seen that with a colorless sample of pure water, shown as the dotted line, all wavelengths of white light, including aU of the red wavelengths, are transmitted through the sample. If we add one drop of red ink to water, to make a solution that appears pale red, the spectrum shows that some of the blue and some of the yellow light 

Absorption of UV /VIS radiation Atomic absorption spectrometry Quantitative elemental analysis 

Emission of Flame photometry, atomic Qualitative and quantitative 

Emission of Atomic fiuorescence Quantitative elemental analysis of 

Emission of UV/VIS radiation Flame photometry, Auger electron spectroscopy (AES) Qualitative and quantitative multielement analysis 

Emission of UV/VIS radiation Atomic fluorescence spectroscopy (AFS) Quantitative elemental analysis of ultratrace concentrations (sub-ppb) 

Absorption of UV/VIS radiation UV/VIS molecular absorption spectroscopy, spectrophotometry Qualitative and quantitative determinations of aromatic and unsaturated organic compounds, inciuding naturai products direct and indirect quantitative determination of inorganic ions, organic molecules, and biochemicals 

Emission of UV/VIS radiation Molecular fluorescence, molecular phosphorescence Detection of small quantities ( ng) of certain aromatic compounds and natural products, analysis of gels and glasses, determination of organic and inorganic species by tagging  

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