Some of the hydrox] groups responsible for these two 
bands without doubt pre-exist in the resin, but others 
are the result of atmospheric water vapor taken up by 
the sample in the course of its preparation (Beck et al., 
1966). The group of more or less well resolved absorp- 
tions near 3.4 » (2950 cm-!) is due to the stretching of 
carbon-hydrogen bonds; the bending motions of these 
same bonds lead to absorption near 6.8 » (1470 cm-!) and 
7.25 pw (1880 cm-!), 
The remaining prominent band in the lower region is 
due to the stretching of carbon-oxygen double bonds. 
This so called carbonyl band usually occurs near 5.8 pu 
(1700 cm:!) in the fossil resins. All these absorption 
bands are almost uniformly typical of all fossil resins and, 
therefore, of limited diagnostic value. Only the position, 
intensity, and resolution of the carbonyl band show sig- 
nificant variation. 
The upper region of the spectra (8 to 16 w; 1250 to 
625 cm-!) is more difficult to interpret in terms of chemi- 
cal structure, but it is nevertheless more useful than the 
lower region because it shows greater variety. Of prime 
importance is the region between 8 and 10 p (1250 and 
1000 cm-!), where absorption is due to carbon-oxygen 
single bonds. Since these vibrations are substantially 
influenced by the carbon skeleton of the entire molecule, 
it is rarely possible to assign these bands to very specific 
structural features. However, as akind of fingerprint of 
a fossil resin, this upper region is the one that we most 
often rely upon to classify resins into groups which are 
not only recognizable as having similar basic structures, 
but which we can increasingly relate to recent resins, and 
thus obtain important evidence about the botanical origin 
of the fossil resins. 
Absorption bands above 10 » (1000 cm-!) are, in gener- 
al, still more difficult to assign and must therefore be used 
[ 69 ] 
