【材料研究方法】光谱分析(英文)

Michelson interferometer

High intensity mercury lamp or heated wire (continuous spectrum)

mirrors, and one movable

Fig. 6-19 Layout of Fourier transform spectrometers

The splitter that is set at an angle of 45" to the path of the collimated partially transmitted The beam is partially transmitted and partially reflected at the thin dielectric beam splitter.

The transmitted and reflected

beams produce interference effects. The beam is then passed through the sample and on to the detector.

Fig. 6-20 The structure of IR spectrometer.

Vibrational spectroscopy

(b)Fourier transform spectrometers ?constructive interference.6.3.11 Instrumentation

Sample

IR source

?destructive interference ?oscillatory pattern or interferogram

Vibrational spectroscopy (b)Fourier transform spectrometers

?mirrors are located equidistant,the optical path difference is an Integral number of 6.3.11 Instrumentation

Integral number of wavelengths

?the reflected beams are in phase

?produce constructive interference

Vibrational spectroscopy

(b)Fourier transform spectrometers

?the optical path difference is an odd number of half 6.3.11 Instrumentation

wavelengths ?destructive interference

monochromatic laser

light sources: argon

ion, krypton ion,

helium-neon gas

Raman scattering: 1 in 109

The scattered light is usually observed at 900to the incident beam.

Fig. 6-21 Infrared dichroism

?

Fig. 6-21 Infrared dichroism

?

Vibrational spectroscopy Infrared Dichroism

Dichroic ratio:

D = A

//

/A⊥D0=2cot2α

f=[3-1]/2=(D-1)(D

+2)/(D

where A

//and A⊥are the absorbances defined with respect to a

reference axis in the sample, typically the orientation direction.

the chain orientation factor. αis the transition moment angle, which is the angle between the direction of the nitrile group’s dipole moment and the chain axis. For PAN, it is 70

the molecular segment relative to the fiber axis