Vertical and adiabatic ionization potentials

One radiation source, the He(Ia) photon energy line, at 21.22 eV, provides vertical and adiabatic ionization potentials. In l,2-dithiole-3-thione (3b), a first ionization band at 8.42 eV has high intensity and is assigned to at least two electronic transitions (75MI43100). Data are also available for other dithiole-3-thiones and two fused dithioles (26) and (27a) (79MI43100). 

Fig. 12). Because the vertical and adiabatic ionization potentials may differ by up to 0 5 eV or sometimes more, thermo-chemical arguments must be consistent in their choice of values. 

Wiberg and coworkers have calculated the vertical and adiabatic ionization potential of 1 in a comparative study including fused cyclopropanes. Using MP4/6-31G(d) and spin contamination corrected UMP4/6-31G(d) energies calculated at MP2/6-31G(d) geometries of the parent compound and radical cation, they obtained an adiabatic ionization potential (relaxation of geometry of the radical cation) of 9.48 eV and a vertical ionization... 

The gas phase ionization potentials (IP) of the nucleobases have been determined by means of photoelectron spectroscopy and photoionization mass spectrometry [32]. Values for the first vertical and adiabatic ionization potentials are summarized... 

Fig. 4.5 A comparison between the vertical and the adiabatic molecular ionization potentials. The parabolas represent the nuclear potential surfaces ofthe molecule and the molecular ion. The horizontal shifts correspond to the different equilibrium nuclear configurations of these species. Electronic energies are measured from the corresponding ground vibrational levels. (IP)v and (IP)a are the vertical and adiabatic ionization potentials, respectively.

Another consequence of the stronger interactions upon ionization is that the equilibrium geometry of the ionized complex may differ signihcantly from that of the neutral states. Broadened ionization onsets are frequently attributed to the spectral superposition of ionization into several vibrational levels for which Franck-Condon factors are more favorable. As a result, the adiabatic ionization potential may be considerably lower than the vertical potential, and the observed ionization onsets may occur above the adiabatic potential. Another factor to be considered is the conformation-dependent efifect, due to the different conformations of the solvent molecules. The most populated form of a complex may involve a less stable form of the solvent. After photoionisation, the lowest-energy dissociation channel in the complex ion leads to the most stable form of isolated solvent, which has to be taken into account for the estimate of the binding energy. 

Fig. 9a, b. A portion of a photoelectron spectrum (idealized) showing (a) the identification of adiabatic and vertical ionization potentials with resolved (1) and unresolved (2) vibrational structures, (b) the identification of a higher adiabatic ionization potential with a break . 

Fio. 12. Fhotoelectron spectrum of methanol vapour using the helium resonance line (21-21 e.v.). Ionization energy increases from left to right. The adiabatic ionization potentials measured (Al-Jobomy and Turner, 1964) are indicated by vertical arrows, and can be compared with (probably) vertical I.P. values derived from electron impact appearance potentials by Collin (1961) (dotted arrows). 

The test set used for most comparisons in the present paper is Database/3 18), which was introduced elsewhere. It consists of 109 atomization energies (AEs), 44 forward and reverse reaction barrier heights (BHs) of 22 reactions, 13 electron affinities (EAs), and 13 ionization potentials (IPs). There are a total of 513 bonds among the 109 molecules used for AEs, where double or triple bonds are only counted as a single bond. Note that all ionization potentials and electron affinities are adiabatic (not vertical), i.e., the geometry is optimized for the ions... 

Figure 3 The photoionization quantum yields (rji) of CH4 as a function of the incident photon energy measured via the double ionization chamber and synchrotron radiation as mentioned in Section 2.1. The bandpass was 0.1 nm, which corresponds to the energy width of 32 meV at the incident photon energy of 20 eV. The vertical ionization potentials of the ionic states involved are indicated by the vertical bars [11] along with the first adiabatic ionization potential by the arrow [17]. (From Ref. [7]. Reprinted with permission from Elsevier Science.)...

The most probable transitions, according to the Franck-Condon principle are the vertical ones. They correspond to the maxima of electron groups in the kinetic spectrum. The upper limits in the kinetic energies for each group correspond to the adiabatic ionization potentials. Thus from the difference of these energy values one can get the difference Ip between the vertical and adiabatic potentials (Table IV). 

Figure 10. Ionization potentials of Si clusters. Solid and dashed lines are the boundaries obtained in experiment. Triangles are the vertical and adiabatic IPs computed using PWB filled for the global minima and empty for some other low-energy neutrals (Ref. [45]).

Reference data on total energies of forms 19-23 optimized by means of different theoretical methods in the gas phase are given in Table 2. Various energetic characteristics of tetrazoles can be successfully estimated. The vertical adiabatic ionization potentials of both neutral tautomers 20 and 21 were calculated for a- and Tt-radical cations <2000CPL(330)212>. The standard molar thermodynamic functions (enthalpies, heat capacities, and entropies) of... 

The effect of a range of substituents on the electron-donor capability of TTFs (tetrathiafulvalenes) was the subject of a report by Bowadt and Jensen <89SM179>. Semiempirical MNDO calculations have been conducted on 5-[l,3]dithiolo[4,5-d]-l,2,3-trithiol-5-ylidine (12) and the following conclusions were adopted the molecule is planar and has Dlh symmetry its vertical ionization potential is 8.61 eV and its adiabatic ionization potential is 8.02 eV. The calculated ionization potentials are in good agreement with the experimental values measured in solution. 

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