Absorbance Spectroscopy: Overview

Abstract

Synonyms Absorbance of light; Transmission of light

Definition Most spectroscopic phenomena arise from the interaction of a molecule with one photon at a time. The molecule may either absorb or scatter the photon; it may also emit a photon. The simplest form of spectroscopy is absorption, which measures how much light of a given frequency is absorbed by a collection of molecules. If a molecule absorbs a photon of frequency ν, it increases its energy by

ΔE = hν = hcλ (1)

where h is Planck’s constant, λ is the wavelength of the light, and c is the speed of light. Only light of the correct frequency to cause a molecule to jump from one energy level to another may be absorbed. When molecules absorb photons of visible or ultraviolet (UV) light, the magnitude of the energy of these photons is (2–12) × 10−19 J/molecule, λ= 170–800 nm which is the amount required to rearrange the valence electron distribution of a molecule. Thus, UV-visible absorption spectroscopy gives... Show more