Ionization potential predicted values

From a comparison with Table 6, one sees that the results of all-electron calculations are lower by about one eV than the ionization potentials predicted by pure -electron theories. In addition, the meaning of the numerical value to be attributed to the additive constants Wzp, is somewhat obscure. This explains why these quantities may be regarded to a certain extent as adjustable molecular parameters, when ionization processes are the main object of a 7i-electron calculation 61>62). 

Now 1 electron-volt is equivalent to 1.6 X 10-12 erg. Hence for an ion of this size the value turns out to be 5 electron-volts. We shall obtain smaller values for larger ions, and larger values for smaller ions. In general, wc find, as predicted above, that the values of (4) agree roughly with the ionization potentials of neutral atoms. 

A critical comparison between experiment and theory is hindered by the range of experimental values reported in the literature for each molecule. This reflects the difficulty in the measurement of absolute ionization cross sections and justifies attempts to develop reliable semiempirical methods, such as the polarizability equation, for estimating the molecular ionization cross sections which have not been measured or for which only single values have been reported. The polarizability model predicts a linear relationship between the ionization cross section and the square root of the ratio of the volume polarizability to the ionization potential. Plots of this function against experimental values for ionization cross sections for atoms are shown in Figure 7 and for molecules in Figure 8. The equations determined... 

One of the main aims of such computations is the prediction and rationalization of the optoelectronic spectra in various steric and electronic environments by either semiempirical or ab initio methods or a combination of these, considering equilibrium structures, rotation barriers, vibrational frequencies, and polarizabilities. The accuracy of the results from these calculations can be evaluated by comparison of the predicted ionization potentials (which are related to the orbital energies by Koopman s theorem) with experimental values. 

Energy levels of heavy and super-heavy (Z>100) elements are calculated by the relativistic coupled cluster method. The method starts from the four-component solutions of the Dirac-Fock or Dirac-Fock-Breit equations, and correlates them by the coupled-cluster approach. Simultaneous inclusion of relativistic terms in the Hamiltonian (to order o , where a is the fine-structure constant) and correlation effects (all products smd powers of single and double virtual excitations) is achieved. The Fock-space coupled-cluster method yields directly transition energies (ionization potentials, excitation energies, electron affinities). Results are in good agreement (usually better than 0.1 eV) with known experimental values. Properties of superheavy atoms which are not known experimentally can be predicted. Examples include the nature of the ground states of elements 104 md 111. Molecular applications are also presented. 

Core Is ionization potentials are calculated by the same methods discussed above for valence ionization potentials. (Note the value for the a, H20 MO, which is the Ola orbital.) For example, SCF calculations with a medium-sized basis set on the above-mentioned fluorocarbons gave predicted Koopmans theorem Is chemical shifts of 2.9, 6.1, 9.4, and 12.7 eV the trend is correctly predicted see C. R. Brundle, M. B. Robin, and H. Basch, J. Chem. Phys., 53, 2196 (1970). Since semiempirical methods like... 

The efficiency and energetics of spectral sensitization by most of the dyes could be correlated with the e v levels of the dyes. He calculated these levels from the ER values, using the linear relation between ER and Nelson s ionization potentials extrapolated to cover all of the dyes. However, quantitative calculations of c)>r on the assumption of direct electron transfer from dye to silver halide predicted values that were much smaller than the experimental ones for the group of dyes with ER... 

In spite of these deviations, the ionization potential rule still has considerable predictive value, although it may be a little too restricted to cover all the addends [116,184], A slight modification of the rule was introduced by Gilbert et al. [12] who proposed that it might be more meaningful to relate the relative effi-ciences of the meta and ortho photocycloaddition with the difference in ionization potential only within a series of structurally very similar alkenes. It was also recognized that ionization potentials relate to properties of the ground state of the reactants rather than of the excited state [185], Nevertheless, the IP rule retains its predictive value in a series in which various arenes are irradiated in the presence of the same alkene [133], Ethyl vinyl ether and benzonitrile (IP = 10.02 eV) yield... 

For photocycloaddition, to benzene the following conclusions were drawn from this empirical correlation [124], Olefins with poor electron-donor or poor electron-acceptor abilities yield mainly meta adducts with benzene (i.e., if AG > 1.4-1.6 eV, all other olefins yield mainly ortho adducts). Even ethene, which had seemed to behave exceptionally, fits into this correlation provided that it acts as the acceptor. The transition area from ortho to meta cycloaddition (i.e., the AG region where ortho meta = 1 1) is relatively large ( 0.2 eV). This is considered not to be surprising because the AG correlation is based on many different types of olefins. When only AG values for derivatives of 1,3-dioxole and for 1,4-dioxene were used, the transition area was narrowed to 0.03 eV. Not only ethene but also vinylene carbonate now fit into the correlation. According to the ionization potential rule, this compound should give only ortho photocycloaddition with benzene. Mattay s empirical rule predicts mainly meta addition, which is indeed found experimentally. 

Recent mass spectral studies confirm the presence of CsAu molecules in the gas phase. From the appearance potentials and the slope of the ionization curve, a dissociation energy of 460 kJ mol-1 was deduced, which agrees well with predicted values for a largely ionic bond. It is also very similar to the value arrived at for CsCl, 444 kJ mol-1 (19a). 

The energies of these two essential orbitals give information, respectively, about the electron-donating properties or ionization potentials and the electron-accepting properties or electron affinities of the compounds. It can be seen that both methods predict that the four tautomers should have remarkably and somewhat surprisingly similar ionization potentials. As may be judged from the known ionization potential of the N(9)H tautomer, whose experimental value is 9.7 eV,98 the PPP-DBP method somewhat underestimates and... 

Concerning the other properties considered in Table XIV the ionization potential of xanthine has been found98 equal to 9.30 eV, a value intermediate, as usual, between those predicted by the PPP and the CNDO methods. The potential predicted for the two tautomeric forms being practically the same, the experimental value does not enable to fix their identity. 

Yokoyama and coworkers investigated the discolouration of titanylphthalocyanine 60, and related porphyrins by silyl radicals derived from methylphenylpolysilane by molecular orbital methods60. Calculated values of AN, the index derived from the hard and soft acids and bases concept was determined from HF/3-21G calculated ionization potentials, electron affinities, and HOMO and LUMO orbital energies of the systems of interest. These studies predict that PhMe2Si should donate an electron readily to 60 to form 60 (equation 18). This prediction is of direct relevance to observations that irradiation of titanylphthalocyanine-coated methylphenylpolysilane films leads to discolouration of the film60. 

---