Absorptivity first overtone region

The general absorptions of methylene groups are illustrated in Figure 2.7, a spectrum of n-decane. 23.1 First Overtone Region — Linear Molecules... 

The 5800-cm peak is usually the strongest peak in the first overtone region of a series of linear hydrocarbons. Tosi and Pinto provide a formula for locating this peak for a series of linear hydrocarbons 5856-85 x weight-fraction of CH2, or about 5800 cm for hexane. They also mention that this peak splits into two closely spaced peaks possibly due to the influence of adjacent methyl groups. The absorptivity of this combined peak does not regularly increase with chain length, probably because it has contributions from two sources. 

C—H Bending Vibrations The C—H bending vibration of alkynes or monosubstituted alkynes leads to strong, broad absorption in the 700-610 cm-1 region. The first overtone of the C—H bending vibration appears as a weak, broad band in the 1370-1220 cm-1 region. 

Individual near-infrared absorption spectra are presented in Figure 13.3 for each of the mixture components. Figure 13.3 presents absorption spectra over the first-overtone and combination spectral regions, respectively. Each spectrum was collected from 100 mM solution of the selected solute dissolved in a pH 6.8 phosphate buffer solution and absorbance was calculated relative to a reference spectrum of the blank phosphate buffer. 

Amerov AK, Chen J, Arnold MA. Molar absorptivities of glucose, water and other biological molecules over the first overtone and combination regions of the near infrared spectrum. Applied Spectroscopy 2004, 58, 1195-1204. 

Figure 6.2-7 Molar absorption coefficient e of pure CO (density 0.15 g cm 127 °C) in the fundamental as well as the first and second stretching overtone regions.

Fig. 6.2-17 shows the absorption in the regions of the first and second overtones of C H stretches in a number of 1-alkenes C5H10, (lowest curve), C6H12, C7H14,... 

Fig. 6.2-18 shows the first and second overtone regions of C- H stretching modes in the near-infrared spectra of three 1-alkynes (CsHg, CeHio, C7H12, from bottom to top). The C-H stretching modes of triply bound C- H groups are shifted to still higher wavenumbers. The first overtone is observed around 6525 cm (Fig. 6.2-18a), and the second overtone is found around 9637 cm (Fig. 6.2-18b). These absorptions are thus distinctly set off from those of C-H groups whose carbon atom is involved in single or double bonds.

Fig. 4.1 The molar absorption coefficient, e, for pure carbon monoxide (at 127 C and 193 bar) in the fundamental, first-overtone, and second-overtone regions.

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