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Infrared Spectroscopy (IR)

Vibrational spectroscopy is an energy sensitive method and is used to characterize compounds in terms of the strengths and number of the bonds present. One can get/detect: the presence of known compounds (finger print) the components of an unknown compound (functional groups)

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Infrared Spectroscopy (IR)

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  1. Vibrational spectroscopy is an energy sensitive method and is used to characterize compounds in terms of the strengths and number of the bonds present. One can get/detect: the presence of known compounds (finger print) the components of an unknown compound (functional groups) and thus a likely structure of a compound changes in the concentration of a species during reaction the properties of bonds (bond strength, force constants) Since a bond in a molecule behaves like a spring, the harmonic/ anharmonic oscillator model is used to describe the 3N-6 or 3N-5 different ways a nonlinear or linear molecule, respectively, consisting of N atoms can vibrate. These vibrational modes (normal modes) give rise to absorption bands of characteristic energies/frequencies/wave numbers, intensities, and widths, which are detected and analyzed. Infrared Spectroscopy (IR)

  2. Vibrational energy levels in harmonic approximation 6. Please note that vibrations normally are more or less anharmonic

  3. Normal modes of vibration 3N – 6 modes (3N – 5 if linear) The three normal modes of H2O and their wavenumbers The four normal modes of CO2

  4. Typical wavenumbers of stretching/bending vibrations

  5. grating, double beam IR - Spectrometer Sample Fourier Transform (FT) Sample

  6. BaSO3 Cs2CrCl5·4H2O KMn(SeO2OH)3 Examples

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