14.8)  The resolution of visible and UV spectra can usually be improved by recording the spectra at low temperature.  Why does this procedure work?

Which of the following statements concerning spectroscopy is correct? A) Concentration of a solution is directly proportional to the % of photons transmitted. B) Salt plates are often used in IR spectroscopic measurements because they are transparent in that region. C) Molar absorptivity is a constant for given species, regardless of concentration or wavelength. D) Fluorescence excitation is usually red-shifted from emission wavelength. E) 2 or more statements are correct. The absorbed energy to enable vibrational level transition falls within which wavelength range A) radio wave B) microwave C) IR D) X-ray E) UV and visible

Why would a chemist using a spectrophotometer need to perform both a scan across all wavelengths and a scan at a specific wavelength?