Interaction between Matter and Infrared Radiation

Interaction between Matter and Infrared Radiation 337 Tab. 10.7 Parameters of various types of infrared burners (Company GoGaS). 

Spectroscopy is the study of the interaction between matter and electromagnetic radiation— radiant energy that displays the properties of both particles and waves. Several different spectrophotometric techniques are used to identify compounds. Each employs a different type of electromagnetic radiation. We will start here by looking at ultraviolet and visible (UVWis) spectroscopy. We will look at infrared (IR) spectroscopy in Chapter 13 and nuclear magnetic resonance (NMR) spectroscopy in Chapter 14. 

Infrared spectra arise from the interaction between matter and electromagnetic radiation of wavelength between about 2 and 50 jjm (respectively 5000 and 200 cm ). The energy associated with such radiations corresponds to transitions between vibrational levels of the ground electronic state of molecule. The absorbance is determined by Beer s law. 

The interaction of electromagnetic radiation with matter in the domain ranging from the close ultraviolet to the close infrared, between 180 and 1,100 nm, has been extensively studied. This portion of the electromagnetic spectrum, called UV/Visible because it contains radiation that can be seen by the human eye, provides little structural information except the presence of unsaturation sites in molecules. However, it has great importance in quantitative analysis. Absorbance calculations for compounds absorbing radiation in the UV/Visible using Beer-Lambert s Law is the basis of the method known as colorimetry. This method is the workhorse in any analytical laboratory. It applies not only to compounds that possess absorption spectra in that spectral region, but to all compounds that lead to absorption measurements. 

In the near and the mid infrared, the absorption of light by matter originates from the interaction between the radiation from a light source and the chemical bonds of the sample. More precisely, if the atoms situated at the two extremes of a bond are different, they form an electric dipole that oscillates with a specific frequency. If such a non-symmetrical bond is irradiated by a monochromatic light source whose frequency is the same as the dipole, then an interaction will occur with the bond. Thus, the electrical component of the wave can transfer its energy to the bond on condition that the mechanical frequency of the bond and the electromagnetic frequency of the radiation are the same (Figure 10.1). This simplified approach can be used to rationalize that in the absence of a permanent... 

The method of infrared (IR) spectroscopy, discovered in 1835 has so far produced a wealth of information on the architecture of matter in our planet and even in the far away stars. Infrared spectroscopy is a powerful technique that allows us to learn more about the structure of materials and their identification and characterization. This study is based on the interaction of electromagnetic (EM) radiation with matter. The EM radiation has energy states comparable to the vibrational energy states of the molecules. These states are included in the energy region between 14000 cm and 100 cm i of the Electromagnetic Radiation, which is divided in three sub-regions called 1) NEAR-IR, o r NIRS 2) MID-IR or MIRS and 3) FAR-IR. or EIRS ... 

Microwaves are electromagnetic radiations lying between radio wave frequencies and infrared frequencies (between 0.3 and 300 GHz). These are produced by a magnetron, which consists of a thermionic diode having an anode and a directly heated cathode. Microwaves contain an electric and a magnetic field component. It is the interaction between the electric field component and the matter that generates the heat through two mechanisms. ... 

Porous substrates (paper, cardboard, wood, plaster, etc.) allow the total elimination of water in the formulations, through diffusion. These are the materials that are best suited to water-based formulations. With substrates that are non-permeable to water (hydrophobic polymer films, metals, etc.), water evaporation is the only solution, but it is difficult to ensme that it is achieved completely, due especially to the very strong interactions that occur between the water and the adhesives polar groups. Optimized formulations, with high dry matter rates (60%, even 70% or 75%), as well as specially developed applicator equipment (hot air drying tunnels, infrared radiation, microwave radiation, etc.,) are designed to solve this problem. 

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