Analytical Chem istry - DePauw University

636 Analytical Chemistry 2.0(a)source(b)sourcesampleFigure 10.63 Distribution of radiationfor (a) Rayleigh, or small-particlescattering, and (b) large-particle scattering.10HSpectroscopy Based on ScatteringThe blue color of the sky during the day and the red color of the sun at sunsetresult from the scattering of light by small particles of dust, moleculesof water, and other gases in the atmosphere. The efficiency of a photon’sscattering depends on its wavelength. We see the sky as blue during the daybecause violet and blue light scatter to a greater extent than other, longerwavelengths of light. For the same reason, the sun appears red at sunset becausered light is less efficiently scattered and is more likely to pass throughthe atmosphere than other wavelengths of light. The scattering of radiationhas been studied since the late 1800s, with applications beginning soonthereafter. The earliest quantitative applications of scattering, which datefrom the early 1900s, used the elastic scattering of light by colloidal suspensionsto determine the concentration of colloidal particles.10H.1 Origin of ScatteringIf we send a focused, monochromatic beam of radiation with a wavelengthl through a medium of particles with dimensions