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Unformatted text preview: 0–8eV energy diﬀerences between excited and ground core nuclear states Mössbauer spectroscopy iden6ﬁca6on of valence states (e.g. Fe2+/Fe3+), site occupancy Summary – Spectroscopic methods Spectroscopic methods are o^en named a^er • the type of interac6on or eﬀect that happens between radia6on and material e.g. emission/absorp6on spectroscopy e.g. Raman, Mössbauer spectroscopy • the range of the electromagne6c spectrum the incident radia6on originates from e.g. infrared, UV-‐VIS, X-‐ray spectroscopy Spectroscopic methods probe the short-‐range order of certain atoms, whereas diﬀrac6on studies the long-‐range order. Infrared (IR) spectroscopy IR spectroscopy, also called vibra6onal spectroscopy, uses the infrared range of the EM spectrum to probe the vibra6onal behavior of minerals. IR radia6on range is o^en divided in 3 subcategories Near-‐IR: 800 – 2500 nm (12500 – 4000 cm–1) Mid-‐IR: 2500 – 25000 nm (4000 – 400 cm–1) Far-‐IR: 25000 – 109 nm (400 – 10 cm–1) ν [cm-‐1] = 107/ λ [nm] applica6ons common in mineralogy: mineral iden6ﬁca6on quan6ﬁca6on of molecule groups, e.g. OH, CO3, NH4 phase transi6on with P and T Infrared (IR) spectroscopy IR spectroscopy is an absorp6on technique. • Radia6on with frequencies in the IR range is passed through a sample. • Molecules, atomic groups, and even the whole laice may interact with the radia6on and partly absorb it. • This promotes the atoms from their ground to the excited vibra6onal state. detector IR source sample Molecular vibra6ons A molecule of N atoms has 3N degrees of freedom. The number of vibra6onal modes is given by 3N-‐6, in case of a linear molecule 3N-‐5. Examples...
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- Fall '13