Electronic Transition in Atoms

Visible UV spanning 300-900 nm contains information on electronic transitions in atoms and molecules. 

The ro-vibronic spectrum of molecules and the electronic transitions in atoms are only part of the whole story of transitions used in astronomy. Whenever there is a separation between energy levels within a particular target atom or molecule there is always a photon energy that corresponds to this energy separation and hence a probability of a transition. Astronomy has an additional advantage in that selection rules never completely forbid a transition, they just make it very unlikely. In the laboratory the transition has to occur during the timescale of the experiment, whereas in space the transition has to have occurred within the last 15 Gyr and as such can be almost forbidden. Astronomers have identified exotic transitions deep within molecules or atoms to assist in their identification and we are going to look at some of the important ones, the first of which is the maser. 

Baer, M. (1983). Quantum mechanical treatment of electronic transitions in atom-molecule collisions, in Molecular Collision Dynamics, ed. J.M. Bowman (Springer, Berlin Heidelberg). 

Another technique that can be used to determine the chemical nature of a thin film is infrared spectroscopy. Some materials will absorb certain frequencies in the infrared (wavelengths 2 to 25 microns) because of the excitation of vibrational energy transitions in molecular species. In the same way that electronic transitions in atoms can absorb radiation of specific frequencies, the vibration of a molecule (stretching or bending) will have a resonance value, and it will be excited by any radiation of this frequency. Consider the H20 molecule and its three vibrational modes, as shown in Figure 17. Clearly, each of these vibrational modes has its own resonant frequency, as indicated, and they are all in the infrared range. 

Vibrational Population in Diatomic Molecules. 18 I 4.2 Rotational Population in Diatomic Molecules, 19 I 4.3 Thermal Contribution to Photolysis and Fluorescence. 20 1-5 Electronic Transition in Atoms, 22... 

X-rays 1 nm-1 pm Inner-shell electron transitions in atoms... 

The electronic transitions in atoms and molecules (and in solids) are associated with two electronic states of the system by the Bohr frequency condition... 

The possibility of using COFj as a fuel for a new class of chemical lasers, utilizing electronic transitions in atoms, radicals or molecules excited as a result of oxidation chain reactions, has also been discussed [134a]. 

A. Kormonicki, T. F. George, and K. Morokuma, Decoupling scheme for a semiclassical treatment of electronic transitions in atom-diatom collisions real valued trajectories and local analytic continuation,/. Chem. Phys. 65 48 (1976). 

UV and visible absorbance spectra arise from electronic transitions in atomic or molecular orbitals (Figure 2.12). 

A most interesting recent development is the work of Augustin and Rabitz, who obtained a transition between statistical and perturbation theories for any type of collision, not only complex-forming ones. More general stochastic aspects of unimolecular reactions have been discussed by Sole and Widom. An application of a phase-space model to electronic transitions in atomic collisions has been reported, as well as a simple RRKM model for electronic to vibrational energy transfer in 0( Z)) -I- Nj collisions. ... 

Infrared (IR) radiation and visible light are used frequently in chemistry labs in spectrometers to analyze molecular vibrations and electronic transitions in atoms, molecules, and salts. These instruments generally pose no safety hazards. 

UV radiation is produced by electron transitions in atoms and molecules, as in a mercury discharge lamp. UV radiation from the sun causes tanning of the skin. Radiation in the UV range can cause florescence in some substances, can produce photographic and ionizing effects, and is easily detected. 

The result is the same whether one chooses to call either of these processes electron transfer followed by transfer of labilized ligand (0 orCl ) or atom transfer resulting in a net electron transfer in the opposite direction. In each case, electron transfer would produce states in which the bond that breaks would have become labilized and the bond formed would have become inert. Electron transfer as the primary action is consistent with the Franck-Condon principle that electron transitions in atomic systems are very rapid compared with nuclear motions, but one cannot experimentally determine that it is primary unless there is detection of intermediate complexes—in this case preceding and following formation of the oxygen or chlorine bridge. 

Electron transitions in atoms can be induced by thermal energy, such as that provided by a flame. Relaxation M --- M can result in the release of a photon of... 

Contents J.M.Bowman Introduction. - D.Secrest Inelastic Vibrational and Rotational Quantum Collisions. -G. C.Schatz Quasiclassical Trajectory Studies of State to State Collisional Energy Transfer in Polyatomic Molecules. - R. Schinke, J. M. Bowman Rotational Rainbows in Atom-Diatom Scattering. - M.Baer Quantum Mechanical Treatment of Electronic Transitions in Atom-Molecule Collisions. - Subject Index. 

The interaction of radiation with matter can take many forms. The photoelectric effect, the Compton effect, and pair generation-armihilation are processes that occur at wavelengths shorter than those encountered in the infrared. Infrared photons can excite rotational and vibrational modes of molecules, but they are insufficiently energetic to excite electronic transitions in atoms, which occur mostly in the visible and ultraviolet. Therefore, a discussion of the interaction of infrared radiation with matter in the gaseous phase needs to consider only rotational and vibrational transitions, while in the solid phase lattice vibrations in crystals must be included. 

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