Moreover, the dairy protein exhibits more resolved bands at 4865 [cm.sup.-1], due to the v(NH)+[delta](NH) combination band, and near 4055 [cm.sup.-1] which could be attributed to the CH functional group as a combination or overtone band .
In addition to those ones, the spectrum of cellulose displays the O-H and C-O stretching combination band at 4400 [cm.sup.-1], the overtone band of CH bending vibration at 4250 cm- with a possible further contribute of C[H.sub.2] stretching and bending combination band and, finally, the combination band of CH and C-O-C stretches and CC vibration positioned at 4010 [cm.sup.-1].
Finally, it can be noticed that the first overtone band of v(C[H.sub.2]) at 5668 [cm.sup.-1] appears well defined only in the spectrum of dragon's blood, whereas the marked noise toward the high wavenumbers does not allow us to discern it in the shellac resin.
As regards near-IR region, combination and overtone bands were not subjected to spectral anomalies; because of the small absorption coefficients, the diffuse contribution results, indeed the dominant factor, in determining the behavior of the NIR reflection bands [6, 27].
Common to all resins are the first overtone bands from methylenic stretching at 5775 (asymmetric) and 5665 (symmetric) [cm.sup.-1], then the weak and broad combination band of v(OH)+[delta](OH) which is centered at around 5170 [cm.sup.-1], and finally the poorly defined band near 4865 [cm.sup.-1].
PC1, shown in Figure 6(b), is characterized by bands associated with drying oils, such as the C[H.sub.2] stretching first overtone band (in the 5700-5800 [cm.sup.-1] spectral range) [6, 8], combination band of methylenic C-H stretching and bending (between 4250 and 4350 [cm.sup.-1]) [6, 8], scissoring mode of methylene (1442 [cm.sup.-1]) [2, 8], and in-phase methylene twist mode (~1302 [cm.sub.-1]) [2, 8].
As regards drying oils, the main near infrared absorption bands are represented by the combination of methylenic C-H stretching and bending (between 4250 and 4350 [cm.sup.-1]) and first C[H.sub.2] stretching overtone bands (in the 5700-5800 [cm.sup.-1] spectral range).
Quantitative data were obtained directly from the intensity of the acrylic overtone band at 1620 nm, which allows very easy calibration of the method.
The overtone band in vinyl ethers is shifted to about 1612 nm, whereas cycloaliphatic epoxies (in contrast to glycidyl ethers) unfortunately do not show a specific overtone or combination band in the near-infrared spectrum which could be used for the monitoring of their conversion.
Possible combination bands are a second OH overtone band at 939 nm (3vOH) and a second harmonic CH overtone band at 1126 nm (3vCH).
(71) have attempted NI glucose detection in two overlapping regions, 750-1050 and 850-1300 nm, which encompass the 3vOH and 3vCH glucose overtone bands. Hiese and co-workers (72-76) and Marbach et al.
Another interesting peak is due to the second C=O overtone of anhydride, which is found in the range between 5300 and 5500 [cm.sup.-1] The overtone bands
are not changed during cure, and therefore the peaks depend only on the content of anhydrides that do not react.