We have formulated the following rules for working out screening (shielding) constants: (1) for each additional electron in http://www.selleckchem.com/products/XL184.html the system, the screening increases by 0.5 unless (2) the electron to be ionized occupies a new orbital such as from beryllium to boron when it increases by 1 and (3) to account for the pairing effect, such as from nitrogen to oxygen, the screening constant increases by 1. For example, for the carbon system, the screening increases by 0.5 units to 3.5 and increases by a further 0.5 to 4 for nitrogen but increases to 5 for oxygen.We made different estimates of the screening constants S2 and S1 and obtained various values of a and b. We then selected the values that give the best results and a list of screening constants, coefficients a and b and reduced masses as shown in Table 2.
They are used with equation (20) to calculated the ionization energies of isoelectronic sequences from five electrons.The values calculated from expression (20) are presented for the first six appropriate members of each series for the following two reasons. Firstly, as we have already shown [14], ionization energies of the first few members of isoelectronic sequences are the most precise. Sometimes, only the first four or five members of a series are experimentally measured and uncertainties increase further along a series. Secondly, our results are compared with ionization energies with those compiled in the CRC Handbook of Chemistry and Physics, and for many isoelectronic series with more than twenty electrons, only a limited number of values are available for each sequence.
Some of these values are given to many significant figures and some only to two or three significant figures because uncertainties can be of the order of 1eV or higher. Since, as with previous work, all our results are rounded to three decimal places we have decided that where the CRC Handbook of Chemistry and Physics has provided values with more than three decimal places they are rounded to three decimal places in the tables.8. Ionization Energies from Five- to Eighteen-Electron Isoelectronic Atomic IonsIonization energies reported in the CRC Handbook for five to eighteen electronic series (first six members) are given in Table 3. Values of ionization energies calculated using our coefficients are provided in Table 4.
Percentage differences between our values and values published by the CRC Handbook as listed in Table 5 show that all values agree to 98% or better. Just over 76%, the calculated values agree to 99% or better.Table 3Ionization energies (eV) Anacetrapib of isoelectronic series from the CRC Handbook (5 to 18 electron sequences)��first six members of each series.Table 4Ionization energies (eV) of isoelectronic series calculated using expression 23 and coefficients/constants from Table 2 (5 to 18 electron sequences).