Other Types of Spectroscopy

In some techniques, including XRD, some IR spectroscopic techniques, and neutron activation, the surface of the soil sample is analyzed using radiation reflected or emitted from the sample. In the other types of spectroscopy, such as NMR, information is obtained from radiation passing through the sample. Infrared spectroscopy (both NIR and MIR) can be used in both transmission and reflection analyses. 

One major advantage of NMR over other types of spectroscopy is that NMR signals are highly specific and quantitative. Because the resonance frequency... 

Noda, I., Generalized 2-dimensional correlation method applicable to infrared, Raman and other types of spectroscopy, Appl Spectrosc., 47, 1329, 1993. 

Robert A. Friedel To Dr. Sharkey s remarks on mass spectroscopy I would like to add a few pertinent comments on other types of spectroscopy which would be applicable to the study of species obtained from coal subjected to plasma, laser irradiation, and similar high energy processes. 

Radiation which induces NMR transitions is usually produced by radiofrequency (RF) coils wound around the sample. These are energized by alternating currents approximately matching the Larmor frequency. The coils are arranged so that the magnetic field of the radiation Bi is perpendicular to the static field Bq. In contrast to other types of spectroscopy, the electric field of the radiation plays no role here. The simplest case is a circularly polarized RF field, such that, in the laboratory frame,... 

Various other types of spectroscopy, such as acoustic spectroscopy and fluorescence spectroscopy, can also be employed for analysis of a sample. Since the characteristics of different materials vary in different respects and over different frequency ranges, a complete analysis of a sample may require the use of a number of spectroscopic (or other) techniques. Also, because information is available regarding the characteristics of various materials, it is not always necessary to understand the quantum mechanical theory behind spectroscopy in order to effectively use the equipment. To understand the fundamental operation of the equipment, however, a thorough knowledge of quantum theory is necessary. 

Thus far, we have examined vibrational spectroscopy using IR absorption spectroscopy, what we called in Ch. 3 one photon method , a general type that encompasses most experiments in spectroscopy. There exist, however, other types of spectroscopy to observe vibrations. These are for instance Raman spectroscopy, which is also of a current use in chemical physics and may be considered a routine method. Other less known methods are modem time-resolved IR spectroscopies. All these methods are two-photon or multiphoton spectroscopies. They do not involve a single photon, as in absorption, but the simultaneous absorption and emission of two photons, as in Raman and in other scattering experiments, or the successive absorption(s) and emission(s) of photons that are coherently delayed in time, as in time-resolved nonlinear spectroscopies. By coherently , we assume the optical waves that carry these two photons keep a well-defined phase difference. In this latter type of spectroscopy, we include all modem set-ups that involve time-controlled laser spectroscopic techniques. We briefly sketch the interest of these various methods for the study of H-bonds in the following subsections. 

Similarly to other forms of molecular spectroscopy, the NMR phenomenon is associated with absorption and emission of energy. Before going into the details of NMR it is useful to compare the energy associated with it with the energy required to produce other types of spectroscopy in the context of the continuous electromagnetic spectrum (Figure 1). 

Fluorescence spectroscopy is often used in analytical chemistry, food analysis, environmental analysis etc. It is a very sensitive spectroscopic technique which can be performed nondestructively and provides qualitative and quantitative information of diverse types of chemical analytes [Andersson Arndal 1999, Aubourg et al. 1998, Beltran et al. 1998a, Bright 1995, Bro 1999, Ferreira et al. 1995, Guiteras et al. 1998, Jensen et al. 1989, Jiji etal. 2000, Ross etal. 1991, Wolfbeis Leiner 1985], This application explains an example of estimating relative concentrations and pure analyte spectra from fluorescence measurements of chemical analytes in mixtures. Similar problems also arise frequently in other types of spectroscopy, in chromatography and other areas. Several names are used for this problem unmixing, curve resolution, source separation etc. Specifically, the application... 

One of the most useful aspects of NMR compared with other types of spectroscopy is the elucidation of spatial geometry. Modem high-held instm-ments give spectra in which the hne structure of the signals is more clearly resolved but may still not always show hrst-order coupling. The analysis of... 

Fourier transform infrared spectroscopy (FTIR) - A technique for obtaining an infrared spectrum by use of an interferometer in which the path length of one of the beams is varied. A Fourier transformation of the resulting interferogram yields the actual spectrum. The technique is also used for NMR and other types of spectroscopy. 

As in other types of spectroscopy, transitions between energy states can be brought about by absorption or emission of electromagnetic radiation of a frequency i that corresponds in energy to AF. Thus, by substituting the Planck relationship E - /iv into Equation 19-4. we obtain the frequency of the radiation required to bring about the transition... 

It Is important to emphasise the fundamental difference between electron spectroscopy (both XPS and AES) and the other types of spectroscopy we have thus far encountered. In electron spectroscopy, thd kjnetic energy of emitted electrons is recorded. The spectrum thus consists of a plot of the number of emitted electrons, or the power of the electron beam, as a function of the energy (or the frequency or wavelength) of the emitted electrons (see Figure 21-2). 

In emission and other types of spectroscopy, on the other hand, the atom must be excited, and for most elements, at presently achievable energies, there is no such thing as complete excitation. One is always... 

However, electron spectroscopy supplies very poor information about structures of molecules and effects by substitution in comparison to infhued (IR), nuclear magnetic resonance (NMR), or mass spectroscopy. On the other hand, UV/Vis spectroscopy is a perfect tool in quantitative photometry and very suitable as a detection principle in chromatography [1]. In Fig. I the total spectrum of electromagnetic radiation is given. The UV/Vis section is enlarged and related to other types of spectroscopy used in analytics. 

Mass spectrometry (MS) differs from the other types of spectroscopy discussed in this chapter, in that it does not depend on transitions between energy states. Instead, a mass spectrometer converts molecules to ions, sorts them according to... 

The basic principles of solid state NMR spectroscopy can be most easily understood by discussing the relevant NMR interactions. In contrast to most other types of spectroscopy NMR has the unique feature, that the full quantum mechanical interaction Hamilton operators (Hamiltonians) of the spin system are usually known. As usual all energies are measured in units of the angular velocity (rad/sec), i.e. all energies are divided by ti. 

Fundamental quantities, such as wavelengths and transition probabilities, determined using spectroscopy, for atoms and molecules are of direct importance in several disciplines such as astro-physics, plasma and laser physics. Here, as in many fields of applied spectroscopy, the spectroscopic information can be used in various kinds of analysis. For instance, optical atomic absorption or emission spectroscopy is used for both qualitative and quantitative chemical analysis. Other types of spectroscopy, e.g. electron spectroscopy methods or nuclear magnetic resonance, also provide information on the chemical environment in which a studied atom is situated. Tunable lasers have had a major impact on both fundamental and applied spectroscopy. New fields of applied laser spectroscopy include remote sensing of the environment, medical applications, combustion diagnostics, laser-induced chemistry and isotope separation. 

---