Atomic Absorption vs Atomic Emission
Absorption and emission of an atom help to identify those atoms and provide much information about them. When absorption and emission spectra of a species are put together, they form a continuous spectrum. Therefore, atomic absorption and atomic emission are complementary to each other.
What is Atomic Absorption?
A colored compound is visible to our eyes in that particular color because it absorbs light from the visible range. In fact, it absorbs the complementary color of the color we see. For example, we see an object as green because it absorbs purple light from the visible range. Thus, purple is the complementary color of green. Likewise, atoms or molecules also absorb certain wavelengths from the electromagnetic radiation (these wavelengths are not necessarily be in the visible range). When a beam of electromagnetic radiation passes through a sample containing gaseous atoms, only some wavelengths are absorbed by the atoms. The absorbed energy is used to excite ground electrons to upper levels in the atom. This is known as electronic transition. The energy difference between the two levels is supplied by the photons in the electromagnetic radiation. Since the energy difference is discreet and constant, the same kind of atoms will always absorb the same wavelengths from the given radiation. An absorption spectrum is a plot drawn between absorbance and wavelength. Sometimes instead of wavelength, frequency or wave number can also be used in the x axis. Log absorption value or the transmission value is also used for the y axis in some occasions. After light passes through an atomic sample, if it is recorded, it is known as an atomic spectrum, and it is characteristic to a type of atom. Therefore, it can be used in identifying or confirming the identity of a particular species. This kind of spectrum will have a number of very narrow absorption lines.
What is Atomic Emission?
Atoms can be excited to higher energy levels by giving energy. The lifetime of an excited state is generally short. Therefore, these excited species have to release the absorbed energy and come back to the ground state. This is known as relaxation. The release of energy may take place as electromagnetic radiation, heat or as both types. The plot of released energy versus wavelength is known as the emission spectrum. Each element has a unique emission spectrum as they have a unique absorption spectrum. So radiation from a source can be characterized by emission. Line spectra occur when the radiating species are individual atomic particles that are well separated in a gas.
What is the difference between Atomic Absorption and Atomic Emission?
• Atomic absorption is where certain wavelengths from the electromagnetic radiation are absorbed by the atoms. Emission is where certain wavelengths are emitted by the atoms.
Absorption occurs upon supplying radiation and emission takes place even in the absence of a radiation source.
By absorbing, the electrons in an atom are excited to a higher energy level. By emission, excited electrons are coming back to a lower level.