Energy state of molecule

The energy states and spectra of molecules are much more complex than those of isolated atoms. In addition to the energies associated with molecular electronic states, there is kinetic energy associated with vibrational and rotational motions. The total energy, E, of a molecule (apart from its translational5 and nuclear energy) can be expressed as the sum of three terms  

Absorption of electromagnetic radiation by molecules occurs not only by electronic excitation of the type described for atoms, but also by changes in the vibrational and rotational energies. 

Both rotations and vibrations of molecules are quantized. This means that only particular values of rotational angular momentum or vibrational energy are possible. We speak of these permitted values of the energies as the vibrational and rotational energy levels. 

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Since the primary photoprocess is absorption of a photon to create a photoexcited molecule, photochemistry and spectroscopy are intimately related. Quantum mechanics has played a vital part in describing the energy states of molecules. 

The possible energy states of molecules of B are different from the possible energy states of molecules of, since the species are different and the molecules are able to take up different energy configurations. 

Absorption spectra for polyatomic molecules, particularly in the condensed state, are considerably more complex than atomic spectra because the number of energy states of molecules is generally enormous when compared with the number of energy states for isolated atoms. The cncr.gy F associated with the bands of a molecule is made up of three components. That is. 

Morrison, J.M. (1957) Application of the mass spectrometer to the study of the upper energy states of molecules. Journal of Applied Physics, 28,1409-1413. 

Microscopic kinetic equations for non-equilibrium reactions are derived in the same way as are the relaxation equations, i.e. in terms of fluxes incoming to and outgoing from a particular quantum state. Transitions in reactive collisions have to be added to those in unreactive collisions. This yields a system of equations describing both the approach to chemical equilibrium and the relaxation over energy states of molecules. For simplification, consider the initial reaction stages neglecting reverse reactions. 

In order to characterize the energy state of molecules present in the plasma an energetic scale of temperature was introduced. Its basic imit is electronvolt eV (leV = 1.602jc 10 J). The model chosen for such a scale... 

Kabo, G.J., Blokhin, A.V., Charapennikau, M.B., Kabo, A.G., and Sevruk, V.M. Thermodynamic properties of adamantane and the energy states of molecules in plastic crystals for some cage hydrocarbons. Thermochim Acta 2000, 345 125-133. 

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