Interpretation of a Spectrum
In the preceding sections discussion has centred on the problem of obtaining a reliable, well-resolved spectrum. Before interpretation of the spectrum is attempted the frequency (wavelength) accuracy must be known, either by pre-calibration of the instrument using ammonia gas, water vapour, indene or polystyrene as references, or by calibration of individual spectra, usually by means of a polystyrene film. The latter procedure requires only a minute or so on most instruments and should be a standard operation with low-cost instruments, or whenever single chart papers are used, since the positioning of the paper on the recording drum constitutes a source of error. Polystyrene calibration (e.g. Figures 13–16) covers effectively the range 4,000–650 cm-1 (2·5–15·4 μ). Positions of the principal bands, in cm-1 and μ units, are presented in Table 7; and the complete spectrum is included here (Figure 20).
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