Electronic Transitions in Diatomic Molecules

Condon E U 1928 Nuclear motion associated with electron transitions in diatomic molecules Phys. Rev. 32 858-72... 

Electronic transitions in diatomic molecules are determined by matrix elements of the dipole operator,... 

E. V. Condon, Nuclear motions associated with electronic transitions in diatomic molecules. Phys. Rev. 32, 858 (1928)... 

Discuss how the vibrational spectrum is influenced in electronic transitions in diatomic molecules considering the Franck-Condon principle. 

The electronic spectra for most diatomic molecules are found in the ultraviolet and visible regions. The electronic transitions are usually accompanied by rotational and vibrational transitions. The following selection rules are obtained for electronic transitions in diatomic molecules ... 

For molecular transitions the matrix elements Dim and Dmf are composed of three factors the electronic transition dipole element, the Franck-Condon factor, and the Honl-London factor (Sect. 1.7). Within the two-photon dipole approximation a co) becomes zero if one of these factors is zero. The calculation of linestrengths for two- or three-photon transitions in diatomic molecules can be found in [243, 244]. 

This chapter begins with a treatment of symmetry and electronic structure in diatomic molecules. The symmetry selection rules for electronic transitions are derived, and vibrational band intensities (cf. Fig. 4.1) are described in terms 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. 

One of the consequences of this selection rule concerns forbidden electronic transitions. They caimot occur unless accompanied by a change in vibrational quantum number for some antisynnnetric vibration. Forbidden electronic transitions are not observed in diatomic molecules (unless by magnetic dipole or other interactions) because their only vibration is totally synnnetric they have no antisymmetric vibrations to make the transitions allowed. 

Most of the infrared laser lines originating from transitions between vibrational-rotational levels in different electronic states of diatomic molecules, e. g. N2, Oj, H, D2, CO, CN, etc., have been meanwhile correctly indentified Some lines and term systems have been found which had never been observed before 354a)... 

In the following, we will discuss a number of different adsorption systems that have been studied in particular using X-ray emission spectroscopy and valence band photoelectron spectroscopy coupled with DFT calculations. The systems are presented with a goal to obtain an overview of different interactions of adsorbates on surfaces. The main focus will be on bonding to transition metal surfaces, which is of relevance in many different applications in catalysis and electrochemistry. We have classified the interactions into five different groups with decreasing adsorption bond strength (1) radical chemisorption with a broken electron pair that is directly accessible for bond formation (2) interactions with unsaturated it electrons in diatomic molecules (3) interactions with unsaturated it electrons in hydrocarbons ... 

Recall that homonuclear diatomic molecules have no vibration-rotation or pure-rotation spectra due to the vanishing of the permanent electric dipole moment. For electronic transitions, the transition-moment integral (7.4) does not involve the dipole moment d hence electric-dipole electronic transitions are allowed for homonuclear diatomic molecules, subject to the above selection rules, of course. [The electric dipole moment d is given by (1.289), and should be distinguished from the electric dipole-moment operator d, which is given by (1.286).] Analysis of the vibrational and rotational structure of an electronic transition in a homonuclear diatomic molecule allows the determination of the vibrational and rotational constants of the electronic states involved, which is information that cannot be provided by IR or microwave spectroscopy. (Raman spectroscopy can also furnish information on the constants of the ground electronic state of a homonuclear diatomic molecule.)... 

Certain transition moment integrals for electronic transitions in homopoiar diatomic molecules can be obtained very simply from overlap integrals,12 lor example ... 

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... 

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