Wave numbers near-infrared region

Absorption in the near infrared region is dominated by changes in vibrational energy levels. A typical wave number is that of the "amide A" band at 3300 cm 1 (3.0 pm wavelength), approximately 1014 s. ... 

There are three main infrared bands, namely, the near, mid-, and far infrared zones. The most commonly used band is the mid-range band covering 50 to 2.5 pm or, in wave numbers, 200 to 4000 cm4. The near infrared band that covers the range of 0.8 to 2.5 pm (wave numbers 12500 cm1 to near 4000 cm4) has overtones that have some importance to polyurethane processing. In this region, real-time studies have been carried out to follow the course of a reaction. (Wave numbers (in cm4) = 10000/wavelength (in pm).) The far infrared range does not have information that is relevant to polyurethane studies. 

Infrared radiation is divided into three regions the near-infrared from 800 to 3 (XX) nanometres, the mid-infrared from 3000 to 25000 nm and the far-infrared from 25000 to 10 nm. These subdivisions are arbitrary, essentially based on available instrumental possibilities but also on the type of information that can be accessed in each of these domains. It is customary to express the units in wave-numbers, v in cm" (v = v/c - I /X where vis the frequency in Hz. c the velocity of light and X the wavelength) which corresponds, for example, to 3 300 to 400 cm" for the mid-infrared. 

Primary length measurements are these days based on optical frequency standards. If one needs a unit of length, for example, a wave-length for interferometric measurement, then one divides the optical frequency by the value of the speed of light (299 792 458 m.s ) as defined in the SI metre. The mise en pratique of the metre [44] lists a number of frequency-stabilised lasers at various wavelengths in the visible and near infrared spectral regions. 

Infrared measurements at high pressures are mainly used to study intramolecular vibrational modes in the near i.r. region, that is, of wave-numbers between 5000 and 500 cm. This characteristic region for the intramolecular frequencies of oscillators is important in the chemistry of... 

The region of the electromagnetic spectrum corresponding to the infrared region varies between wave numbers of 12,800-10 cm or 2 = 0.108-1000 pm. This region is divided into three parts, called near-, mid-, and far-infrared [32]. 

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