There are many spectroscopic techniques applicable to the identification and measurement of molecular species (including polyvalent ions and metal–ligand complexes). These can be grouped in different ways, and applied – with varying degrees of complexity – to the study of gas, liquid, and solid phase samples. The following table provides a short summary of the principle molecular spectroscopy techniques used in analytical chemistry:

TechniqueModeSpectral RegionEnergy Transition Sample phase
absorption, reflectanceUV & visible
(near IR)
electronic (vibrational)solution (gas)
Fluorescenceemission (luminescence)UV & visible electronic (vibrational) solution (solid)
PhosphorescenceUV & visible
(near IR)
electronic (vibrational) solution (solid)
Fourier transform infraredabsorption, reflectanceIR vibrational (rotational)solid, gas (solution)
Ramanscatteringsolid, solution
Microwaveabsorptionmicrowaverotational liquid, solution
Electron Spin Resonanceradio wave electron spin statesolution, liquid, solid
Nuclear Magentic Resonance nuclear spin state