Ionization energy/potential

The ionization potential energy, IP, of alkylbenzenes calculated by MOPAC was used as the standard, and it was almost constant for a series of alkyl compounds. The difference in the ionization potential, AIP, of other compounds from that of alkylbenzenes was calculated. The relationship between A log k and AIP is given by ... 

Li), 16956 cm (Na), 12985 cra (K), 12578 cra (Cs)] do not contribute to the thermal functions below 1006 K there is only a translational contribution below this temperature. Above this approximate temperature, the thermal functions become increasingly sensitive to the partition function cutoff procedure used, due to the combined effect of the observation of atomic energy levels of high principal quantum number and a low ionization potential. Energy levels have been observed up to n = 42 (Li), 59(Na), 79(K), 77(Rb), and 73(Cs). However, not all predicted levels have... 

Multistep laser photoionization has been applied to determine a number of important physical properties of heavy atoms with complex spectra including ionization potentials, energy levels, lifetimes of... 

Techniques of stepwise laser excitation and photoionization have been applied to study spectroscopic properties of neutral atoms of lanthanides and actinides. The spectroscopic properties that can be determined include the ionization potential, energy levels, isotope shifts, hyperfine structure, lifetimes of energy levels, branching ratios and oscillator strengths. We discuss the laser methods used to obtain these properties (with emphasis on ionization potentials) and give examples of results obtained for each. The ionization potentials obtained by laser techniques are in eV Ce, 3.3387(4) ... 

See also Pyrrole derivatives Inductive forces (energies), 47-48 Ionization potentials (energies), 51-52 See also Charge transfer vs. adsorption energy, 329-330 aromatic hydrocarbons, 69 Isomer separations, see Chapter 11 Isotherm, adsorption, 52-55... 

Since the extravalent d orbitals of sulfur, selenium, and tellurium are not occupied in the normal states of the free atom, their implicit functional form is determined by another criterion. The values of a number of molecular properties including ionization potentials, energies of electronic transitions, and overlap populations have been examined as a... 

Ionization energy or ionization potential Energy required to remove the most loosely held electron from an isolated atom in the gas phase in order to form a positive ion in the gas phase. More positive ionization potentials indicate that the electron is more tightly held. 

Ionization potential Energy required to detach an electron from an isolated gaseous atom of the element. 

The ionization potential (energy to remove one electron) of a helium atom in its ground state is 24.58 eV. a. What effective nuclear charge does this correspond to Corr5)are with the Z value from the simple variation calculation. 

The principles of ion themiochemistry are the same as those for neutral systems however, there are several important quantities pertinent only to ions. For positive ions, the most fiindamental quantity is the adiabatic ionization potential (IP), defined as the energy required at 0 K to remove an electron from a neutral molecule [JT7, JT8and 1191. 

So, within the limitations of the single-detenninant, frozen-orbital model, the ionization potentials (IPs) and electron affinities (EAs) are given as the negative of the occupied and virtual spin-orbital energies, respectively. This statement is referred to as Koopmans theorem [47] it is used extensively in quantum chemical calculations as a means for estimating IPs and EAs and often yields results drat are qualitatively correct (i.e., 0.5 eV). 

This quantity is found to be related to the local polarization energy and is complementary to the MEP at the same point in space, making it a potentially very useful descriptor. Reported studies on local ionization potentials have been based on HF ab-initio calculations. However, they could equally well use semi-empirical methods, especially because these are parameterized to give accurate Koopmans theorem ionization potentials. 

Quantum chemical descriptors such as atomic charges, HOMO and LUMO energies, HOMO and LUMO orbital energy differences, atom-atom polarizabilities, super-delocalizabilities, molecular polarizabilities, dipole moments, and energies sucb as the beat of formation, ionization potential, electron affinity, and energy of protonation are applicable in QSAR/QSPR studies. A review is given by Karelson et al. [45]. 

In eonPast to the low-Ievel ealeulations using the STO-3G basis set, very high level ealeulations ean be earried out on atoms by using the Complete Basis Set-4 (CBS-4) proeedure of Petersson et al. (1991,1994). For atoms more eomplieated than H or He, the first ionization potential (IP[) ealeulation is a many-eleePon ealeulation in which we ealeulate the total energy of an atom and its monopositive ion and determine the IP of the first ionization reaetion... 

Here P°g,v is a eonstant (having energy units) eharaeteristie of the bonding interaetion between X i and Xv its value is usually determined by foreing the moleeular orbital energies obtained from sueh a qualitative orbital treatment to yield experimentally eorreet ionization potentials, bond dissoeiation energies, or eleetronie transition energies. 

Semiempirical methods are parameterized to reproduce various results. Most often, geometry and energy (usually the heat of formation) are used. Some researchers have extended this by including dipole moments, heats of reaction, and ionization potentials in the parameterization set. A few methods have been parameterized to reproduce a specific property, such as electronic spectra or NMR chemical shifts. Semiempirical calculations can be used to compute properties other than those in the parameterization set. 

The electron alfinity (FA) and ionization potential (IP) can be computed as the difference between the total energies for the ground state of a molecule and for the ground state of the appropriate ion. The difference between two calculations such as this is often much more accurate than either of the calculations since systematic errors will cancel. Differences of energies from correlated quantum mechanical techniques give very accurate results, often more accurate than might be obtained by experimental methods. 

The electron alfinity and ionization potential can be either for vertical excitations or adiabatic excitations. For adiabatic potentials, the geometry of both ions is optimized. For vertical transitions, both energies are computed for the same geometry, optimized for the starting state. 

Another technique for obtaining an ionization potential is to use the negative of the HOMO energy from a Hartree-Fock calculation. This is called Koopman s theorem it estimates vertical transitions. This does not apply to methods other than HF but gives a good prediction of the ionization potential for many classes of compounds. 

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