1) 拉曼谱峰比较尖锐，识别混合物，特别是识别无机混合物要比红外光谱容易。
2) 在鉴定有机化合物方面，红外光谱具有较大的优势，主要原因是红外光谱的标准数据库比拉曼光谱的丰富。
3）在鉴定无机化合物方面，拉曼光谱仪获得400cm^-1以下的谱图信息要比红外光谱仪容易得多。所以一般说来，无机化合物的拉曼光谱信息量比红外光谱的大。
4）拉曼光谱与红外光谱可以互相补充、互相佐证。

以下为石英和方解石的红外光谱及拉曼光谱

 

 

付里叶变换红外光谱仪

Nicolet Nexus Fourier Transform Infrared Spectroscopy (FTIR)
型号：Nexus
生产厂家：美国热电尼高力公司(Thermo Nicolet)

 

附件：红外显微镜，傅立叶变换拉曼光学系统，拉曼显微，欧米采样器，衰减全反射，
漫反射，镜反射，变温红外附件，偏振器

主要技术指标：
1 波长范围：近红外10000～4000cm^-1 (1～2.5μm)
中红外 4000～400cm^-1 (2.5～25μm)
远红外 400～50cm^-1 (25～200μm)

2 最高分辨率：0.019cm^-1
3 信噪比：33000/1
4 快速扫描：1次/秒
5 显微红外：可检测样品大小：10μm；可进行点，线，面扫描
6 FT-Raman光学系统：激发激光光源为Nd:YVO4，是近红外光源，波长为1064nm，波数为9393.6 cm^-1，拉曼显微可检测样品大小：100μm

红外光谱通过测量分子的振动和转动光谱来研究分子的结构和性能，它广泛应用于地质学、化学、医药、材料科学、环境保护等行业，例如：无机、有机化合物，高分子聚合物、矿物和材料。红外显微镜可测量微量及微区样品的光谱信息。傅立叶变换拉曼光学系统可测量各种物质的拉曼谱图。

（中红外光谱仪+远红外光谱仪+近红外光谱仪+红外显微镜+付里叶变换拉曼光谱仪+6万多张可用于全谱自动对比分析的红外光谱标准谱库）

下图为正己烷的红外光谱（gif 动画图片）

Short Theory
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Any engineering physicist knows that electrons will exist only in certain allowed energy states. If an electron in a particular material decides to move from one energy level to another it will generally be (extreme circumstances like the heat death of the universe excepted) in a fashion recognized from past observation. Again molecular bonds can be regarded as quasi-particles with their own allowed energy levels and states also known from past observation. By passing an IR field through a substance we can take note of the specific energy bands absorbed by the sample and from these infer the characteristics of the sample. Actually that was the work of engineering physicists in the earlier part of this century, we just have to match the form of our spectra against the previously mentioned libraries of spectra. What could be easier.

FT-IR Applications
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The infrared absorption spectrum of a material can be used to identify the chemical bonds in the substance. Each substance produces a unique infrared absorption spectrum and this can be used to identify the substance. Information about the types of chemical bonds in the substance can also be gained as each type of chemical formation has its own infrared characteristics. Just as spectral analysis, FTIR allows for the identification of organic and inorganic substances in the solid, liquid and gaseous states. The technique is also used to find the relative composition of the components in an unknown mixture.

The broad number of applications for FTIR is virtually limitless. Just a few applications include:

Environmental engineers use FTIR in order to assess the state of some site the engineer must ascertain the types and quantities of contaminants that reside there. As one amongst many methods, FTIR can play a role in this assessment.

Biologists such as those working on the human genome project can use FTIR in order to identify genes within strands of DNA. DNA, a long chain of organic compounds, can be sliced and its IR spectrum can be analyzed. Various genes have characteristic chemical bonds and these can be seen using FTIR. Older more time consuming methods of chromatography are being replaced by these quicker FTIR methods.

Chemical engineers use FTIR to identify compounds and measure their concentrations.

Plant Engineers use FTIR in order to monitor concentrations and levels of any number of good and bad gasses and contaminants.

 

激光共聚焦显微拉曼光谱仪

Laser Confocal Raman Microscope,英国雷尼绍公司生产

型号：

我校2004年购置的InVia型显微激光拉曼光谱仪，是英国Renishaw公司生产的高精度物理分析仪，也是目前国际上同类仪器的先进产品。与传统的色散型激光拉曼光谱仪相比，新型拉曼光谱仪在两个方面做了重大改进：一是检测技术，二是滤除瑞利线的技术。传统的色散型拉曼光谱仪（如U-1000型、SPEX1403型等）使用光电倍增管检测器，仪器工作时，步进马达驱动光栅转动，让拉曼散射谱线逐点通过光电倍增管的检测窗口，获得一张信噪比好的谱图需要很长时间。新型的拉曼光谱仪采用CCD检测器（Charge Coupled Device，即电荷耦合型检测器），一次可检测一段谱区，大大提高了检测速度。由于采用了CCD检测器和陷波滤波(Notch Filter)技术，使新型的拉曼光谱仪变得非常小巧。传统的拉曼光谱仪从激光激发样品直至光电倍增管检测，大约需要经过10米的光程，拉曼信号衰减严重，需用大功率激光激发样品来提高信号强度。而新型的拉曼光谱仪从激光激发样品至CCD检测，中间的光程不到一米，信号强度和检测效率大大提高，一般只需用10mW左右的小功率激光激发样品，检测一个样品一般也只需要几分钟时间。另外，小功率激光对样品的损害大大减小，使用拉曼光谱的应用领域大大拓宽。

与红外光谱一样，拉曼光谱也是用来检测物质分子的振动和转动能级，所以这两种光谱俗称姊妹谱。但两者的理论基础和检测方法存在明显的不同。我们说物质分子总在不停地振动，这种振动是由各种简正振动叠加而成的。当简正振动能产生偶极矩的变化时，它能吸收相应的红外光，即这种简正振动具有红外活性；具有拉曼活性的简正振动，在振动时能产生极化度的变化，它能与入射光子产生能量交换，使散射光子的能量与入射光子的能量产生差别，这种能量的差别称为拉曼位移(Raman Shift)，它与分子振动的能级有关，拉曼位移的能量水平也处于红外光谱区。

拉曼光谱仪与红外光谱仪的检测原理大不相同。红外光谱法的检测直接用红外光检测处于红外区的分子的振动和转动能量：用一束波长连续的红外光透过样品，检测样品对红外光的吸收情况；而拉曼光谱法的检测是用可见激光（也有用紫外激光或近红外激光进行检测）来检测处于红外区的分子的振动和转动能量，它是一种间接的检测方法：把红外区的信息变到可见光区，并通过差频（即拉曼位移）的方法来检测。由于可见光区是电子跃迁的能量区，当用可见激光激发样品时，电子跃迁所产生的光致发光信号会对拉曼信号产生干扰，严重时，拉曼信号会被完全淹没。光致发光信号的特点是谱带较宽，最高强度处的波长（或频率）一定。根据这个特点，拉曼光谱仪一般都配备多种激光器，当一种激光激发样品时产生很强的光致发光干扰信号时，就改用另一种激光，目的是避开光致发光的干扰。我校新购的这台激光拉曼光谱仪，配有三种激光：氩离子激光器的514.5nm激光、氦氖激光器的632.8nm激光、和二极管激光器的785nm激光，是这几年国内所引进的拉曼光谱仪中，激光种类配备较全的一台。下图为某有机物分别在514.5nm和632.8nm激光激发下的拉曼光谱，比较表明该样品在632.8nm激光激发下受荧光的干扰较小。

仪器性能指标：
测试范围：
1)使用氩离子激光器，50-9400cm^-1
2)使用氦氖激光器，100-5800cm^-1
3)使用二极管激光器，100-3200cm^-1
最小测试面积：1平方微米；
分辨率：1-2cm^-1（随选用的光栅不同而不同）。

该仪器可对固态、液态、气态的有机或无机样品进行非破坏性分析，如用于岩石矿物组成、矿物固液气相包裹体、宝玉石、高聚物、无机非金属材料等的鉴定。

正面图

背面图

若换上100倍物镜，可对粒径小至1微米的样品进行检测

石英样品的拉曼光谱测试过程

二水石膏(CaSO₄.2H₂O)的拉曼光谱

该拉曼光谱仪上配备的高低温（液氮温度-600℃)样品台

Introduction
-----------------
When light is scattered from a molecule or crystal, most photons are elastically scattered. The scattered photons have the same energy (frequency) and, therefore, wavelength, as the incident photons. However, a small fraction of light (approximately 1 in 10⁷ photons) is scattered at optical frequencies different from, and usually lower than, the frequency of the incident photons. The process leading
to this inelastic scatter is termed the Raman effect. Raman scattering can occur with a change in vibrational, rotational or electronic energy of a molecule. If the scattering is elastic, the process is called Rayleigh scattering. If it’s not elastic, the process is called Raman scattering.

Raman scattering (or the Raman effect) was discovered in 1928 by V.C. Raman who won the Nobel prize for his work. If the substance being studied is illuminated by monochromatic light, for example from a laser, the spectrum of the scattered light consists of a strong line (the exciting line) of the same frequency as the incident illumination together with weaker lines on either side shifted from the strong
line by frequencies ranging from a few to about 3500 cm-1. The lines of frequency less than the exciting lines are called Stokes lines, the others anti-Stokes lines. Raman spectroscopy is very important practical tool for quickly identifying molecules and minerals.

A Raman spectrometer was deployed on the Viking landers in 1972 and in other missions. Raman spectroscopy also has important scientific applications in studying molecular structure.