SPECTROSCOPY,Textbook and reference,Textbook Kenneth A Rubinson & Judith F Rubinson, Contemporary Instrumental Analysis(现代仪器分析), 科学出版社 Gary D. Christian, Analytical Chemistry, 3rd Ed., John Wiley & SonsReference 武汉大学化学系编，仪器分析，高等教育出版社,2001 于世林、李寅蔚主编，波谱分析法 （全国轻化工类高等学校工业分析专业系列教材）重庆大学出版社，1994年第2版 西北师院、陕西师大、河北师大、上海师大、华中师大、河北师院编，有机分析教程 陕西师大出版社，1987年第1版 苏克曼、潘铁英、张玉兰，波谱解析法 华东理工大学出版社，2002.8,Chapter 1 Introduction 1. Spectroscopy,What is spectroscopy?A typical spectroscopy experiment is extremely simple to describe. Electromagnetic radiation at some frequency is allowed to interact with the sample of interest. Then some property of that radiation is measured, for example the amount absorbed, diffracted, emitted, scattered, etc. The frequency of radiation to be used is determined by the energy levels associated with the property of the sample we are interested in such as electronic levels, rotational motion, vibrational motion, etc.,Spectroscopy includes UV-Vis spectrometry (Ultraviolet/visible Absorption Spectrometry), IR spectrometry (Infrared Spectrometry), NMR (Nuclear Magnetic Resonance Spectroscopy) and MS (Mass Spectrometry) Rapid and precise analytical methods for organic compounds Only applied for pure compound Hyphenated techniques (GC-MS, GC-IR, LC-MS, LC-NMR etc.) for mixture analysis,2. Electromagnetic spectrum,The wave is described with wavelength and frequency Electromagnetic radiation possess a certain amount of energy. The energy of one unit of the radiation, the photon, is related to the frequency byE = hvE is the energy of the photon in ergs, h is Plancks constant, 6.62 x 10-27 erg sec,The electromagnetic spectrum,The electromagnetic spectrum is very wide and covers radiation from gamma-rays to visible light to radiofrequency waves. The visible region is that narrow region of the electromagnetic spectrum to which the color sensors in our eyes are sensitive. This region, which covers wavelengths of 300 nm to 800 nm, has energies which are just below the carbon-carbon bond strength.,g-rays,g-rays are also known to cause tissue damage. These are very high energy electromagnetic waves and are often generated during decay of radioactive materials. Usually some dense material like lead is necessary to keep them contained. Aside from their use in radioactive labelling experiments, they are also used in Mossbauer spectroscopy which is used to investigate nuclear structure. The fact the g-rays can destroy a nuclei also make them useful for probing properties of nuclei.,X-rays,X-rays can cause damage to tissue and usually interact with living matter by breaking bonds. The energies associated with x-rays are definitely above the bond energies. This is why they are used in the treatment of localized tumors and they are also known to increase the risk of cancer as well. X-rays are used to study biological molecules through several processes such as scattering and diffraction. Biophysical applications of x-rays are concerned mostly with the diffraction experiment where detailed information about biopolymer structure can be obtained. X-rays can be used for this mainly because its wavelength (typically used are the Ka band of Cu, 1.54A, or Mo, 0.71A) is on the order of the length of a chemical bond. We often talk of the type of X-rays used in wavelengths on the angstrom level or in terms of their energies.,Ultraviolet radiation,invisible electromagnetic radiation between visible violet light and X rays; it ranges in wavelength from about 400 to 4 nanometers and in frequency from about 10 15 to 10 17 hertz. It is a component (less than 5%) of the suns radiation and is also produced artificially in arc lamps, e.g., in the mercury arc lamp.,Visible light,The visible region of the electromagnetic spectrum consists of photons with wavelengths from approximately 400 to 700 nm. The short wavelength cutoff is due to absorption by the lens of the eye and the long wavelength cutoff is due to the decrease in sensitivity of the photoreceptors in the retina for longer wavelengths. Light at wavelengths longer than 700 nm can be seen if the light source is intense.,Infrared radiation IR,If we travel the other direction down the electromagnetic spectrum from visible light, we discover the infrared region. This region can be used to sense heat since it generates heat as a by-product of the vibrations it induces. IR is used to investigate vibrational modes of molecules. It is usually measured in wave numbers (cm-1) which is the inverse of the wavelength of the IR radiation.,Microwaves,Microwaves can be used to investigate the rotational properties of molecules as well as electron spin properties. EPR & NMR. At these frequencies, there is no appreciable spontaneous emission and we must rely on the surroundings to provide or absorb the energy to attain equilibrium. All emissions are now stimulated. This applies both to NMR and EPR. Unlike other spectroscopies, we can change the sensitivity not only by temperature but also by increasing the magnetic field used to split the spin energy levels. We are allowed to fine tune the Boltzmann distribution. This is only one of the reasons NMR spectroscopist keep buying more powerful magnets.,