Calculated and experimental energies

There was less agreement between calculated and experimental energy values. The use of 6-3IG, the best procedure in energy calculations of three-membered rings, yielded a value too low by more than 40 kJ moF in the case of diazirine bond separation energy was calculated as -45 kJ moF the experimental value is +0.4 kJ moF . Vibrational correction and extrapolation to 0 K would reduce this difference by several kJ moF . 

TABLE 3.4. Calculated" and Experimental Energies of Valence Electrons and Two-Electron Ions E (au)... 

The unsigned average deviation between calculated and experimental energies is 0.36 kcal/mol for a collection of 35 benzenoid molecules. This result does not include 7,12-dimethylbenz[a]anthracene (36) the discrepancy of 16 kcal/mol between theory and experiment is in all likelyhood due in part to an error in the latter. Although certainly real, steric interactions involving the methyl group in position 12 are probably not so severe as to cause a destabilization exceeding that found in 1,8-dimethylnaphthalene and 4,5-dimethylphenanthrene—molecules that are discussed further below. 

Table 12 Calculated and Experimental Energy Levels in Pyridines and Related Aromatic Compounds...

Thus one-center integrals can be estimated by comparing calculated and experimental energies for a sufficiently large number of appropriate states of the isolated atom. 

Thus, for P and some neutral S-related complexes in natural silicon, the absorption of about 24 parity-allowed transitions is observed. One can note that while differences exist between the calculated and experimental energy levels, the differences between the corresponding experimental energy spacings... 

In making this table, the basis set used consisted of 63 generalized Sturmians. Singlet and triplet states were calculated simultaneously, 0.5 s of 499 MHz Intel Pentium III time being required for the calculation of 154 states. Experimental values are taken from the NIST tables (http //physics.nist.gov/asd). Discrepancies between calculated and experimental energies for the ions may be due to experimental inaccuracies, since, for an isoelectronic series, the accuracy of the generalized Sturmian method increases with increasing atomic number. 

Configuration interaction and spin-dependent interactions Section 3.1.1 provides a basic framework for computing free-ion energies and eigenfunctions. When the simple Coulomb and spin-orbit interactions are used, however, discrepancies of the order of a few hundred wave numbers remain between calculated and experimental energy levels. A more complete free-ion Hamiltonian includes the following additional interactions ... 

The C3H7 cation has been studied in the gas phase by mass spectrometry, and the heats of formation and relative energies are given in Table 2. The 2-propyl cation is the most stable species, but it is difficult to make an exact comparison between the calculated and experimental energies because of the large experimental errors. 

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