Raman
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拉曼光谱与红外光谱分析方法比较
拉曼光谱
红外光谱
光 谱 范 围 40-4000C m -1
光 谱 范 围 400-4000C m -1
水可作为溶剂
样品可盛于玻璃瓶，毛细管等容器 中直接测定
固体样品可直接测定
水不能作为溶剂 不能用玻璃容器测定 需要研磨制成 KBR 压片
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拉曼光谱分析法
刘和文
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Remote Raman Analysis on Planetary Missions
To allow Raman spectroscopy at range of 10's of meters.
This NASA-funded project is aimed at Mars landers or landers on other planets, but also has terrestrial uses.
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Some Raman Advantages
Here are some reasons why someone would prefer to use Raman Spectroscopy. • Non-destructive to samples (minimal sample prep) • Higher temperature studies possible (don’t care about IR radiation) • Easily examine low wavenumber region: 100 cm-1 readily achieved. • Better microscopy; using visible light so can focus more tightly. • Easy sample prep: water is an excellent solvent for Raman. Can probe sample through transparent containers (glass or plastic bag).
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Watch for Fluorescence
Spectrum of anthracene. A: using Ar+ laser at 514.5 nm. B: using Nd:YAG laser at 1064 nm.
• a series of anti-Stokes shifted peaks (still lower intensity, shorter wavelength)
• spectrum independent of
excitation wavelength (488,
632.8, or 1064 nm)
Shift back away from FT-Raman to dispersive Raman with multichannel detector systems.
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Infrared and Raman Spectra of Benzene
IR
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IR Absorptions
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Rayleigh / Raman Transitions and Spectra
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Rayleigh / Raman Transitions and Spectra
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The Spectrum
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SpCeHcEtrNuLmI of CCl4, using an Ar+ laser at 488 nm.
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Raman Spectroscopy
Another spectroscopic technique which probes the rovibrational structure of molecules.
E=h(0 + ) 产 生 反 stokes 线 ； 弱；
h(0 - ) E1 V=1 E0 V=0
STOKES
Raman位移：
Raman 散 射 光 与 入
射光频率差；
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h0 h(0 + ) h
ANTI-STOKES
Rayleigh
0
0 +
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Rayleigh / Raman Transitions
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激光拉曼光谱基本原理
Rayleigh散射：
激发虚态
h(0 - )
弹性碰撞；
无能量交换，仅
改变方向； Raman散射：
h0
非弹性碰撞
E1 + h0 E0 + h0
h0 h0
h0 +
； 方 向 改 变 且 有 E1
V=1
能量交换；
E0
V=0
Rayleigh散射
Raman散射 h
A complete Raman spectrum consists of:
• a Rayleigh scattered peak (high intensity, same wavelength as excitation)
• a series of Stokes-shifted peaks (low intensity, longer wavelenreceived Nobel Prize in 1931.
Can probe gases, liquids, and solids.
Must use a laser source for excitation.
Resurgence in recent years due to the development of new detectors with improved sensitivity.
E0基态， E1振动激发态； E0 + h0 ， E1 + h0 激发虚态；
获得能量后，跃迁到激发虚态.
（1928年印度物理学家Raman C V 发现；1960年快速发展）
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基本原理
1. Raman散射 E1 + h0
Raman散射的两种 E2 + h0
跃迁能量差：
E=h(0 - ) 产 生 stokes 线 ； 强 ；基态分子多；