Lecture10

Can idendfy materials based on their vibradonal

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Unformatted text preview: ral lines Sharp lines at specific wavelengths indicate the presence of parDcular molecules Ozone layer mapping Photo: NASA Satellite map of O3 over AntarcDca DetecDng absorpDon of light in the far ­infrared region of the electromagneDc spectrum (THz region) VibraDons in solids •  QuanDzed vibraDons in solids are called phonons. •  CharacterisDc vibraDons are signatures of complex interacDons between many atoms. •  Can idenDfy materials based on their vibraDonal spectrum. Complex THz mo8on in crystals Low ­frequency coupled mode in sucrose – 1.9 THz Comparison: Mid ­IR vibraDon Localized O ­H stretch vibra8on in sucrose – near 100 THz Sucrose 50 -1 -1 Absorption coefficient [cm M ] 60 40 30 20 10 0 1,0 1,5 2,0 2,5 3,0 Frequency [THz] 3,5 4,0 THz spectra of illicit substances 10 10 cocaine morphine 8 6 6 4 4 2 2 0 Absorption αd 8 0 0.5 1.0 1.5 2.0 2.5 3.0 1...
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