Two more features worth noticing in the Figure 3.6B are the fluctuations in the baseline and the baseline itself, which is not horizontal. The small fluctuations in the baseline are referred to as noise. Noise is the manifestation of the random weak signals generated by the instrument electronics. To identify the sample peaks clear of the noise, the intensity of the sample peaks has to be at least 3-4 times higher than the noise. A better signal-to-noise ratio is obtained by recorded more than one spectra and averaging; the noise being random gets cancelled out. Instrumental factors are responsible for the non-horizontal baseline observed in Figure 3.6B: The light sources used in the instruments emit radiations of different intensities at different wavelengths and usually the detector sensitivity is also wavelength-dependent. A reasonable horizontal baseline for the samples can easily be obtained by subtracting the spectrum obtained from the solvent the sample is dissolved in.

Other features of the spectroscopy and the spectra obtained will be discussed as and when they arise in the following lectures.