The Infrared Region

The infrared (from the Latin, infra, meaning below red) region of the spectrum corresponds to frequencies from just below the visible frequencies to just above the high- 

The position of an infrared band is specified by its wavelength (A), measured in microns (jam). A micron (or micrometer) corresponds to one millitxith (10 ) of a meter, or 1cm. A more common unit, however, is the wavenumber (v), which corresponds to the number of cycles (wavelengths) of the wave in a centimeter. The wavenumber is the reciprocal of the wavelength (in centimeters). Since 1 cm = 10,000 jam, the wavenumber can be calculated by dividing 10,0(X) by the wavelength in microns. The units of the wavenumber are cm reciprocal centimeters). 

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The aromaticity factor (ratio of the number of aromatic carbons to the total number of carbons), identical to that given by the ndM method or the Brandes method in the infrared region. 

As the wavelength moves into the infrared region, it is more common to change units from nanometers to micrometers (microns). For example. 10,600 nm would be written as 10.6 pm. 

Neodymium and YAG Lasers. The principle of neodymium and YAG lasers is very similar to that of the ruby laser. Neodymium ions (Nd +) are used in place of Cr + and are often distributed in glass rather than in alumina. The light from the neodymium laser has a wavelength of 1060 nm (1.06 xm) it emits in the infrared region of the electromagnetic spectrum. Yttrium (Y) ions in alumina (A) compose a form of the naturally occurring garnet (G), hence the name, YAG laser. Like the ruby laser, the Nd and YAG lasers operate from three- and four-level excited-state processes. 

The range of photon energies (160 to 0.12 kJ/mol (38-0.03 kcal/mol)) within the infrared region corresponds to the energies of vibrational and rotational transitions of individual molecules, of electronic transitions in many semiconductors, and of vibrational transitions in crystalline lattices. Semiconductor electronics and crystal lattice transitions are beyond the scope of this article. 

When doped, low band-gap polymers have optical transitions in the infrared region of the spectmm, and therefore transmit more visible light in the conducting form than in the insulating form. This feature enables this class of conducting polymers to be investigated for a number of optical appHcations where both electrical conductivity and optical transparency are desired. 

The noncontact measurement principle, usually called optical or radiation temperature measurement, is based on detecting electromagnetic radiation emitted from an object. In ventilation applications this method of measurement is used to determine surface temperatures in the infrared region. The advantage is that the measurement can be carried out from a distance, without contact with the surface, which possibly influences the heat balance and the temperatures. The disadvantages are that neither air (or other fluid) temperature nor internal temperature of a material can be measured. Also the temper-... 

Stretching vibration in the infrared region. The imine salts possess an active hydrogen, whereas their quaternization products exhibit the same spectral properties as the enamine salts (187). 

The blue colour of oxygen in the liquid and solid phases is due to electronic transitions by which molecules in the triplet ground state are excited to the singlet states. These transitions are normally forbidden in pure gaseous oxygen and, in any case, they occur in the infrared region of the spectrum at 7918 cm" ( Ag) and 13 195 cm" ( ]+). However, in the condensed phases a... 

The infrared region of the electromagnetic spectrum may be divided into three main sections 34... 

For molecules in which at least one internal rotating part has a dipole moment component perpendicular to the axis of rotation, there should appear directly in the infrared spectrum transitions between the torsional states. For most cases these would be quite far in the infrared region and therefore more difficult to observe. Nevertheless a few molecules of this type have been studied in this region, and such transitions have been reported.6... 

It is fortunate, however, that there are small amounts of other gases in the atmosphere, notably carbon dioxide and water vapour. Both these gases absorb strongly in the infrared region of the reflected radiation, keeping the heat... 

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