拉曼光谱分析法
合集下载
相关主题
- 1、下载文档前请自行甄别文档内容的完整性，平台不提供额外的编辑、内容补充、找答案等附加服务。
- 2、"仅部分预览"的文档,不可在线预览部分如存在完整性等问题,可反馈申请退款(可完整预览的文档不适用该条件!)。
- 3、如文档侵犯您的权益，请联系客服反馈,我们会尽快为您处理(人工客服工作时间：9:00-18:30)。
➢ Symmetric stretching vibrations are much stronger scatterers than asymmetric stretching vibrations
Raman 散 射 光 与 入
射光频率差； 0 -
h0 h(0 + ) h
ANTI-STOKES
Rayleigh
0
0 +
Rayleigh / Raman Transitions
IR Absorptions
Rayleigh / Raman Transitions and Spectra
Rayleigh / Raman Transitions and Spectra
The Spectrum
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 wavelength)
拉曼光谱分析法
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；
E=h(0 + ) 产 生 反 stokes 线 ； 弱；
h(0 - ) E1 V=1 E0 V=0
STOKES
Raman位移：
红外活性和拉曼活性振动
①红外活性振动 ⅰ永久偶极矩；极性基团； ⅱ瞬间偶极矩；非对称分子；
红外活性振动—伴有偶极矩变化的振动可以
产生红外吸收谱带.
②拉曼活性振动
eE
诱导偶极矩 = E
r
非极性基团，对称分子；
wenku.baidu.com
e
拉曼活性振动—伴随有极化率变化的振动。
对称分子：
对称振动→拉曼活性。
不对称振动→红外活性
Spectrum of CCl4, using an Ar+ laser at 488 nm.
Raman Spectroscopy
Another spectroscopic technique which probes the rovibrational structure of molecules. C.V. Raman discovered in 1928; received 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. Shift back away from FT-Raman to dispersive Raman with multichannel detector systems.
Selection Rule for Raman Scattering
❖ Must be change in polarizability
➢ Non-Polar groups such as C-S, S-S, C=C, C C (triple bond), N=N and heavy atoms (I, Br, Hg) strong scatterers
Infrared and Raman Spectra of Benzene
IR
Raman
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
Watch for Fluorescence
Spectrum of anthracene. A: using Ar+ laser at 514.5 nm. B: using Nd:YAG laser at 1064 nm.
Want to use short wavelength because scattering depends on 4th power of frequency. …BUT… Want to use long wavelength to minimize chance of inducing fluorescence.
• a series of anti-Stokes shifted peaks (still lower intensity, shorter wavelength)
• spectrum independent of excitation wavelength (488, 632.8, or 1064 nm)
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).
Raman 散 射 光 与 入
射光频率差； 0 -
h0 h(0 + ) h
ANTI-STOKES
Rayleigh
0
0 +
Rayleigh / Raman Transitions
IR Absorptions
Rayleigh / Raman Transitions and Spectra
Rayleigh / Raman Transitions and Spectra
The Spectrum
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 wavelength)
拉曼光谱分析法
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；
E=h(0 + ) 产 生 反 stokes 线 ； 弱；
h(0 - ) E1 V=1 E0 V=0
STOKES
Raman位移：
红外活性和拉曼活性振动
①红外活性振动 ⅰ永久偶极矩；极性基团； ⅱ瞬间偶极矩；非对称分子；
红外活性振动—伴有偶极矩变化的振动可以
产生红外吸收谱带.
②拉曼活性振动
eE
诱导偶极矩 = E
r
非极性基团，对称分子；
wenku.baidu.com
e
拉曼活性振动—伴随有极化率变化的振动。
对称分子：
对称振动→拉曼活性。
不对称振动→红外活性
Spectrum of CCl4, using an Ar+ laser at 488 nm.
Raman Spectroscopy
Another spectroscopic technique which probes the rovibrational structure of molecules. C.V. Raman discovered in 1928; received 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. Shift back away from FT-Raman to dispersive Raman with multichannel detector systems.
Selection Rule for Raman Scattering
❖ Must be change in polarizability
➢ Non-Polar groups such as C-S, S-S, C=C, C C (triple bond), N=N and heavy atoms (I, Br, Hg) strong scatterers
Infrared and Raman Spectra of Benzene
IR
Raman
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
Watch for Fluorescence
Spectrum of anthracene. A: using Ar+ laser at 514.5 nm. B: using Nd:YAG laser at 1064 nm.
Want to use short wavelength because scattering depends on 4th power of frequency. …BUT… Want to use long wavelength to minimize chance of inducing fluorescence.
• a series of anti-Stokes shifted peaks (still lower intensity, shorter wavelength)
• spectrum independent of excitation wavelength (488, 632.8, or 1064 nm)
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).