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1、傅立叶红外光谱介绍,电磁波,Gamma Ray,X-Ray,UV,Infrared,Micro Wave,Short Wave,Radio Waves,Energy eV,Wavenumber cm-1,Wavelength m,Visible,光与分子的作用,分子激发产生振动,振动的种类?,伸缩振动,对称伸缩振动,不对称伸缩振动,例如: 水,变形振动,水的红外图,1500,2000,2500,3000,3500,wavenumber cm-1,60,65,70,75,80,85,90,95,100,Transmission %,正己烷,50多不同的振动,正己烷,指纹区“,红外光谱分为三个范围
2、:,15.000 cm-1,4.000 cm-1,400 cm-1,5 cm-1,NIR,MIR,FIR,如何得到一张图,色散型红外光谱仪,傅立叶变换红外光谱仪,色散型红外光谱仪,Detector,Detector,优点: - 不需要计算机,缺点: - 速度慢 - 光通量低 = 灵敏度低 (S/N ratio),傅利叶变换红外光谱仪原理,x,Detector,x,L,L + x,例 1: x =0, 相长干涉,结果,1. Beam part (定镜),2. Beam part (动镜),x,L,L + x,例 2: x =1/2, 相消性干涉,0,结果,1. Beam part (定镜),2.
3、 Beam part (动镜),x,L,L + x,example 3: x = , constructive Interference,0,Resulting signal,1. Beam part (fixed),2. Beam part (movable),x,L,L + x,example 4: x =3/2, destructive Interference,0,Resulting signal,1. Beam part (fixed),2. Beam part (movable),Mirror motion,Intensity,监测器信号,Frequence,Intensity,光
4、源,单色光源,单色光源的调制信号,Entstehung des Interferogramms,Frequence,Intensity,9条单一频率的光源,检测器信号,Frequency,Intensity,红外光源,X, moving mirror,Intensity,干涉图的来源,透射光谱,1.) In the empty sample compartment an Interferogram is detected. The result of the FOURIER transformation is R().,Fourier-Transformation,500,1000,1500,
5、2000,2500,3000,3500,4000,wavenumber cm-1,0.10,0.20,0.30,0.40,Single channel intensity,X, moving mirror,Detector intensity,2.) A second interferogram is detected with the sample placed in the sample compartment. The result of the FOURIER transformation is S(). S() shows similarities to the reference
6、spectrum R(v), but has lower intensities at the regions the sample absorbs radiation.,Fourier-Transformation,500,1000,1500,2000,2500,3000,3500,4000,wavenumber cm-1,0.10,0.20,0.30,0.40,Single channel intensity,X, moving mirror,Detector intensity,透射光谱,The transmission spectrum T() is calculated as the
7、 ratio of the sample and reference single channel spectra: T() = S()/R().,透射光谱,Absorbance Transmission - Why?,Transmission,Absorbance,T() = S()/R(),Lambert-Beers law: AB = -log (S()/R() AB = c b,Principle layout of FT-IR spectrometer,x,Layout of an FT-IR spectrometer (TENSOR series),Electronic,Sourc
8、e compartment,Sample compartment,Sample position,Detector,Interferometer compartment,Aperture wheel Filter wheel,NIR: Source : tungsten lamp Optical material : Quartz Detector: Ge, InGaAs MIR: Source: Globar Optical material: KBr, ZnSe Detector: DTGS, MCT FIR: Source : Globar, Hg lamp Optical materi
9、al : PE, CsI Detector: DTGS, Bolometer,Differences between NIR, MIR, FIR,Optical components:,Fourier Transformation (FT),Data acquisition results in a digitized interferogram, I(x), which is converted into a spectrum by means of the mathematical operation called a Fourier Transform (FT). The general
10、 equation for the Fourier Transform is applicable to a continuous signal. If the signal (interferogram) is digitized, however, and consists of N discrete, equidistant points, then the discrete version of the FT (DFT) must be used: S(k . ) = I(n x) exp (i2k n/N) The continuous variables x and have be
11、en replaced with n Dx and k D , representing the n discrete interferogram points and the k discrete spectrum points. The fact that we now have a discrete, rather than continuous, function, and that it is only calculated for a limited range of n (i.e. the measured interferogram has a finite length) l
12、eads to important effects known as the picket-fence effect and leakage.,The Fourier Transform,x,高光谱分辨,低光谱分辨,添零,The picket-fence effect occurs if the interferogram contains frequency components which do not exactly coincide with the data point positions, k. , in the spectrum. The effect can be though
13、t of as viewing the spectrum through a picket fence, thereby hiding those frequencies that are behind the pickets, i.e. between the data point positions k. . In the worst case, if a frequency component is exactly between two sampling positions, a signal reduction of 36% can occur. The picket-fence e
14、ffect can be reduced by adding zeros to the end of the interferogram (zero filling) before the DFT is performed. This interpolates the spectrum, increasing the number of points per wavenumber. The increased number of frequency sampling positions reduces the error caused by the picket-fence effect. G
15、enerally, the original interferogram size should always be at least doubled by zero filling, i.e. zero filling factor (ZFF) of two is chosen. Zero-filling interpolates using the instrument line-shape, and in most cases is therefore superior to polynominal or spline interpolation methods that are applied in the spectral domain.,Zero-filling factor 2,Zero-filling factor 8,截趾函数,In a real measurement, the interferogram can only be measured for a finite distance of mirro
