Atomic spectroscopy is the determination of elemental composition by its electromagnetic or mass spectrum. The study of the electromagnetic spectrum of elements is called Optical Atomic Spectroscopy. Electrons exist in energy levels within an atom. These levels have well defined energies and electrons moving between them must absorb or emit energy equal to the difference between them. In optical spectroscopy, the energy absorbed to move an electron to a more energetic level and/or the energy emitted as the electron moves to a less energetic energy level is in the form of a photon. The wavelength of the emitted radiant energy is directly related to the electronic transition which has occurred. Since every element has a unique electronic structure, the wavelength of light emitted is a unique property of each individual element. As the orbital configuration of a large atom may be complex, there are many electronic transitions which can occur, each transition resulting in the emission of a characteristic wavelength of light, as illustrated below. Show  Energy Transitions The science of atomic spectroscopy has yielded three techniques for analytical use: Atomic Absorption. Atomic Emission. Atomic Fluorescence. The process of excitation and decay to the ground state is involved in all three fields of atomic spectroscopy. Either the energy absorbed in the excitation process, or the energy emitted in the decay process is measured and used for analytical purposes. How the three techniques are implemented. If light of just the right wavelength impinges on a free, ground state atom, the atom may absorb the light as it enters an excited state in a process known as atomic absorption. This process is illustrated on the right.Atomic absorption measures the amount of light at the resonant wavelength which is absorbed as it passes through a cloud of atoms. As the number of atoms in the light path increases, the amount of light absorbed increases in a predictable way. By measuring the amount of light absorbed, a quantitative determination of the amount of analyte element present can be made. The use of special light sources and careful selection of wavelength allow the specific quantitative determination of individual elements in the presence of others. The atom cloud required for atomic absorption measurements is produced by supplying enough thermal energy to the sample to dissociate the chemical compounds into free atoms. Aspirating a solution of the sample into a flame aligned in the light beam serves this purpose. Under the proper flame conditions, most of the atoms will remain in the ground state form and are capable of absorbing light at the analytical wavelength from a source lamp. The ease and speed at which precise and accurate determinations can be made with this technique have made atomic absorption one of the most popular methods for the determination of metals. The atomic absorption process In atomic emission, a sample is subjected to a high energy, thermal environment in order to produce excited state atoms, capable of emitting light. The energy source can be an electrical arc, a flame, or more recently, a plasma. The emission spectrum of an element exposed to such an energy source consists of a collection of the allowable emission wavelengths, commonly called emission lines, because of the discrete nature of the emitted wavelengths. This emission spectrum can be used as a unique characteristic for qualitative identification of the element. Atomic emission using electrical arcs has been widely used in qualitative analysis.Emission techniques can also be used to determine how much of an element is present in a sample. For a "quantitative" analysis, the intensity of light emitted at the wavelength of the element to be determined is measured. The emission intensity at this wavelength will be greater as the number of atoms of the analyte element increases. The technique of flame photometry is an application of atomic emission for quantitative analysis. ICCD Quantum Efficiency relevant to Atomic spectroscopy The third field of atomic spectroscopy is atomic fluorescence. This technique incorporates aspects of both atomic absorption and atomic emission. Like atomic absorption, ground state atoms created in a flame are excited by focusing a beam of light into the atomic vapor. Instead of looking at the amount of light absorbed in the process, however, the emission resulting from the decay of the atoms excited by the source light is measured. The intensity of this "fluorescence" increases with increasing atom concentration, providing the basis for quantitative determination.The source lamp for atomic fluorescence is mounted at an angle to the rest of the optical system, so that the light detector sees only the fluorescence in the flame and not the light from the lamp itself. It is advantageous to maximize lamp intensity since sensitivity is directly related to the number of excited atoms which in turn is a function of the intensity of the exciting radiation. While atomic absorption is the most widely applied of the three techniques and usually offers several advantages over the other two, particular benefits may be gained with either emission or fluorescence in special analytical situations.
The light which atoms give off is made up of specific wavelengths, called lines; observed by a spectroscope, the lines are, collectively, atomic spectra. In more detail … In an atom, electrons have specific and discrete energies. There are many more energy states (or levels) in each atom than there are electrons. When an electron transitions (‘jumps’) from one energy level to another, it emits (if going from a higher level to a lower one) or absorbs (vice versa) light – a photon – with a discrete, specific wavelength. In any given set of conditions (pressure, temperature, magnetic field strength, etc), the collection of all those specific wavelengths is the spectrum of the atom … so atomic spectra are the spectra of atoms! As the atomic electron energy levels are unique to each element, the lines in a spectrum (emission or absorption) can be used to identify the elements present in the source (a star, say) or gas between the source and us (e.g. the interstellar medium). Of course, for an extragalactic object – a quasar, perhaps – you need more than one line to make a certain identification … because the universe is expanding (and so you don’t know how much just one line may have been redshifted). The light electronic transitions in atoms produces may not be in the visual part of the electromagnetic spectrum, but for atoms that are neutral or have lost only one or two electrons (yes, ‘atomic spectra’ refers to the line spectrum of ions too!), most lines are in the UV, visual, or near infrared. For highly ionized atoms, the lines are found in the extreme UV or x-ray region. As the relative intensity of the lines in an atomic spectrum varies with temperature, analysis of the lines in the spectrum of a star (say) can give an estimate of the temperature of the star’s surface (photosphere). The width of the lines depends on the pressure of the gas; the structure of the lines depends on the magnetic field strength; the … (you get the idea) – atomic spectra are a wonderful window into the physical conditions of places far, far away! Looking for more? This University of Oregon webpage has a good, brief, description of atomic spectra; and Physics Lab’s Atomic Models and Spectra covers both the historical context and a bit more of the theory. As atomic spectra play such a vital role in optical astronomy, no wonder there are so many Universe Today articles involving atomic spectra! Here’s a random selection: New Study Find Fundamental Force Hasn’t Changed Over Time, Spitzer Discovers Early Galaxy Forming Region, and Strange Nebula Around Eta Carinae . The Astronomy Cast episode Energy Levels and Spectra is all about atomic spectra. Other Astronomy Cast episodes well worth a listen, in regard to atomic spectra, include Optical Astronomy and In Search of Other Worlds. Sources:
Atomic spectra are a series of lines corresponding to different colors. The lines represent the electromagnetic radiation emitted or absorbed by an atom. We know that in an atom, electrons have discrete and specific energies. There are more energy states in an atom than there are electrons. When an electron transitions from one energy level to another, it emits light or photon with a specific wavelength. In any given set of conditions, the collection of all these specific wavelengths is what constitutes the atomic spectrum. Hence, atomic spectra are the spectra of atoms. Here, in this short piece of article, we will be looking at atomic spectra more in detail along with the Rydberg formula and the spectral series of the hydrogen atom. Atomic spectra are defined as The spectrum of the electromagnetic radiation emitted or absorbed by an electron during transitions between different energy levels within an atom. When an electron gets excited from one energy level to another, it either emits or absorbs light of a specific wavelength. The collection of all these specific wavelengths of the atom in a given set of conditions like pressure, temperature, etc is the atomic spectra of atoms. There are three types of atomic spectra and they are emission spectra, absorption spectra, and continuous spectra. You might want to check the difference between emission and absorption spectra for a better understanding. From the image above, it is evident that the atomic hydrogen emission spectrum is divided into a number of spectral lines with wavelengths given by the Rydberg formula. The observed spectral lines in the hydrogen emission spectrum are due to the atomic transitions between different energy levels. The spectral series are important in astronomical spectroscopy.
Rydberg FormulaUsing the Rydberg formula, it becomes easy to calculate the spectral lines. Following is the formula:
Where, R is the Rydberg constant (1.09737*107 m-1) Z is the atomic number n is the upper energy level n’ is the lower energy level λ is the wavelength of light Spectral series of single-electron atoms like hydrogen have Z = 1. Following is the table for λ in vacuum:
Following is the table for λ in the air:
Atomic SpectroscopyAtomic spectroscopy is the study of the electromagnetic radiation absorbed or emitted by atoms. There are three types of atomic spectroscopy and they are:
Uses of Atomic Spectroscopy
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Atomic spectra are defined as the spectrum of the electromagnetic radiation emitted or absorbed by an electron during transitions between different energy levels within an atom.
Types of atomic spectra are :
Types of atomic spectroscopy are:
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