Spectrum absorption electromagnetic

Infrared spectroscopy has proven to be a very informative and powerful technique for the characterization of zeolitic materials. Most infrared spectrometers measure the absorption of radiation in the mid-infrared region of the electromagnetic spectrum (4000-400 cm or 2.5-25 xm). In this region of the spectrum, absorption is due to various vibrational modes in the sample. Analysis of these vibrational absorption bands provides information about the chemical species present. This includes information about the structure of the zeolite as well as other functional... 

Molecular absorption spectroscopy deals with measurement of the ultraviolet-visible spectrum of electromagnetic radiation transmitted or reflected by a sample as a function of the wavelength. Ordinarily, the intensity of the energy transmitted is compared to that transmitted by some other system that serves as a standard. 

Not all vibrations and rotations are infrared-active. If there is no change in dipole moment, then there is no oscillating electric field in the motion, and there is no mechanism by which absorption of electromagnetic radiation can take place. An oscillation, or vibration, about a center of symmetry, therefore, will not be observed in the infrared spectrum (absorption) but can be observed in the Raman spectrum (scattering). 

NIR (near infra red) spectroscopy — Besides optical absorption in the UV-Vis region of the electromagnetic spectrum, absorption in the near infrared region can be employed to study electrochemical processes. This part of the electromagnetic spec-... 

Due to electron transitions within the 4f level, all of the lanthanide (Ln " ) ions, with the exception of lanthanum (III) and lutetium (III) which have closed-shell configurations, absorb radiation at ultraviolet or visible wavelengths of the electromagnetic spectrum. Absorptivities are not high, however, and because of shielding the absorption spectra do not, on the whole, show significant changes upon complexation of the Ln " ion. 

Our atmosphere is not transparent to all wavelengths of the electromagnetic spectrum. Absorption in the Earth s atmosphere occurs by different molecules. 

Microwave spectroscopy began in 1934 with the observation of the -20 GHz absorption spectrum of ammonia by Cleeton and Williams. Here we will consider the microwave region of the electromagnetic... 

The determination of an analyte s concentration based on its absorption of ultraviolet or visible radiation is one of the most frequently encountered quantitative analytical methods. One reason for its popularity is that many organic and inorganic compounds have strong absorption bands in the UV/Vis region of the electromagnetic spectrum. In addition, analytes that do not absorb UV/Vis radiation, or that absorb such radiation only weakly, frequently can be chemically coupled to a species that does. For example, nonabsorbing solutions of Pb + can be reacted with dithizone to form the red Pb-dithizonate complex. An additional advantage to UV/Vis absorption is that in most cases it is relatively easy to adjust experimental and instrumental conditions so that Beer s law is obeyed. 

A dye molecule has one or more absorption bands in the visible region of the electromagnetic spectrum (approximately 350-700 nm). After absorbing photons, the electronically excited molecules transfer to a more stable (triplet) state, which eventually emits photons (fluoresces) at a longer wavelength (composing three-level system.) The delay allows an inverted population to build up. Sometimes there are more than three levels. For example, the europium complex (Figure 18.15) has a four-level system. 

The electromagnetic spectrum measures the absorption of radiation energy as a function of the frequency of the radiation. The loss spectrum measures the absorption of mechanical energy as a function of the frequency of the stress-strain oscillation. 

Table 3.1 summarizes the details of typical sources, absorption cells, dispersing elements and detectors used in different regions of the electromagnetic spectrum. 

Spectrometers are designed to measure the absorption of electromagnetic radiation by a sample. Basically, a spectrometer consists of a source of radiation, a compartment containing the sfflnple through which the radiation passes, and a detector. The frequency of radiation is continuously varied, and its intensity at the detector is compar ed with that at the source. When the frequency is reached at which the sample absorbs radiation, the detector senses a decrease in intensity. The relation between frequency and absorption is plotted as a spectrum, which consists of a series of peaks at characteristic frequencies. Its interpretation can furnish structural information. Each type of spectroscopy developed independently of the others, and so the data format is different for each one. An NMR spectrum looks different from an IR spectrum, and both look different from a UV-VIS spectrum. 

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