(精选)【医学英文课件】 Vibrational (Infrared and Raman) Spectroscopy And NMR, MRI教学课件.ppt

Vibrational (Infrared and Raman) Spectroscopy And NMR, MRI;*;*;;;region of infrared that is most useful lies between2.5-25 mm (4000-400 cm-1) depends on transitions between vibrational energy states :stretching and bending;Molecular Excitation Modes;Molecular Vibrations;Fingerprint of Molecule;IR Stretching Frequencies: What Do they Depend On?;Quantum mechanics: The frequency (?) depends on the energy gap between vibrational levels E = h??= hc/??(cm-1);An Infrared Spectrometer;Dipole Moment Must Change during for a vibration to be “IR active”!;What type of vibrations would occur in pentane?;IR spectrum;What can we learn from IR spectroscopy?;Inelastic scattering of light at a molecule;Sir Chandrashekhara Venkata Raman;Principles of Raman Spectroscopy;When a sample is irradiated with monochromatic light (e. g. with laser light using discrete lines between 300 and 1064 nm) Different physical phenomena happen: 1. The main part of the incident light is transmitted without interaction 2. Roughly 10-4 part of the light is elastically scattered with no energy absorption ---Rayleigh line 3. A part of the incident light may be absorbed by electronic transitions and is emitted as --- Flourescence 4. Only 10-8 of the incident light is inelastically scattered and interacts with the sample . The energy is partly absorbed --- Raman spectrum; Raman spectrometer. Monochromatic light is passed through a concentrated sample. Scattered light (dashed lines) is collected with the aid of a curved mirror. This is then diffracted through a monochromator which allows the identification of frequencies due to both Rayleigh and Raman scattering. Note that the lower mirror reflects transmitted light back through the sample to double the intensity of scattered light.;But dominant process is elastic scattering: Rayleigh scattering ?— ? ?— ? ? Photon in Photon out No vibration No vibration If incident photon energy E; vibration energy v, then in terms of energy,