A large number of analytical techniques exploit spectroscopy in one form or another, and provide a range of tools for both the identification (qualitative analysis) and measurement (quantitative analysis) of atoms, ions, and molecules. Spectroscopic methods can be used alone or, in many cases, coupled with chromatography to achieve both the separation and measurement of multicomponent samples.

The science of the interaction of energy, in the form of electromagnetic radiation (EMR), acoustic waves, or particle beams, with matter.
The measurement of the intensity (I) of radiation, in the form of EMR or high energy particles (electrons, ions, etc.), with some form of electronic device.
An instrument that can measure radiation intensity as a function of energy (E), frequency (ν), wavelength (λ), wavenumber (σ), etc. in order to obtain a spectrum
A spectrometer that uses a photon detector to measure the ratio of the radiant power incident on (P0) and emergent from (P) a sample of matter, as a function of photon wavelength (λ), frequency (ν), wavenumber (σ) or energy (Ephoton).

Spectroscopy and the Electromagnetic Radiation:

Spectroscopic techniques can be classified according to the type – or range – of energy interacting with the sample. This in turn determines what types of samples can be analysed, and the nature of the information that can be obtained. As you can see from the diagram below, high energies allow you to probe individual atoms, allowing elemental analysis to be performed; lower energies allow you to probe bonds, functional groups, and molecular motion (mainly vibration and rotation). We can therefore broadly classify spectroscopic techniques into atomic and molecular.

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We can also look at the nature of the interaction: when EMR encounters matter, it can at a minimum be absorbed, reflected, scattered, and/or transmitted. Absorption of energy (chemical, EMR, electrical, kinetic, etc.) can also result in the emission of electromagnetic radiation. Techniques can thus be further classified as to whether they involve absorption, emission, reflectance, etc. This site will describe a number of these techniques, and provide virtual tours of representative instrumentation.