Molecular orbital crossing

When molecular orbital cross sections oi are available, photoionization intensities are more conveniently obtained as (11,12)... 

A covalent bond is formed when an electron pair is shared between atoms. According to valence bond theory, electron sharing occurs by overlap of two atomic orbitals. According to molecular orbital (MO) theory, bonds result from the mathematical combination of atomic orbitals to give molecular orbitals, which belong to the entire molecule. Bonds that have a circular cross-section and are formed by head-on interaction are called sigma (cr) bonds bonds formed by sideways interaction ot p orbitals are called pi (77-) bonds. 

The study of the photoionization cross section as a function of photon energy for the different orbitals of Me4Sn, which can be a powerful tool for the assignment of the spectra and the analysis of the contribution of the various atomic orbitals to the molecular orbitals, has been carried out by the authors of References 11 and 12 by using He I and He II as ionizing source, and of Reference 13 by using synchrotron radiation. Bertoncello... 

Equations (16) and (17) were then used to calculate the molecular orbital contributions to and - just as Oddershede and Sabin did in their more accurate calculations - a table for the velocity-dependence of core, bond, and lone-pair contributions to Se for protons was constructed [25,42], These results together with equation (10) lead to the calculation of the proton stopping cross section in compound materials with chemical binding effects incorporated. 

FIGURE 3. Pertinent molecular orbitals for the electronic excitation by the CIEEL process of the crossed-conjugated oxyanions m-17a and m-17b derived from the monocychc (m-15a) and bicyclic (m-15b) dioxetane, as calculated by the AMI method. Reprinted with permission from Reference 34b. Copyright (2000) American Chemical Society... 

Figure 18 De-excitation cross sections of Ne( P2) by M (M = CH4, SiH4, GeH4, CF4, and Sip4, Ar, Kr, Xe, H2, D2, N2, O2, CO, NO, CO2, N2O, and SFs) as a function of the polarizability of M. (From Ref 155.) The target molecules are classified by the type of their outermost molecular orbitals c-type ( ) re-type (O) and nonbonding (O).

At energies higher than 10 keV, ionization cross sections were calculated using Seltzer s formula [183]. Seltzer s formula gives the partial ionization cross sections for five molecular orbitals of water. The total ionization cross sections in the energy range of 10 keV to 10 MeV were obtained by summing up all the partial cross sections (Fig. 8). 

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