Ionization adiabatic and vertical

The ionization being accompanied by a vibrational excitation, the fine structure of bands can be exploited for determination of vibrational levels of an ionized system in the ground and excited states. Of course, the first (0-0) and the strongest vibrational bands are the most important because they determine adiabatic and vertical ionization potentials of radicals. 

FIGURE 4.1 Illustration of adiabatic and vertical ionization potentials. Adiabatic I.P. refers to the energy difference between the lowest quantum states of the molecule and its positive ion. Often, Franck-Condon (vertical) transitions lead to a higher value, the vertical ionization potential. 

Table 3.5. Adiabatic and vertical ionization energies of small molecules (cf. Table 3.4), compared with Koopmans -theorem (KT) estimates using MO or NBO orbital energies, and with experimental adiabatic values...

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 . 

Photoelectron spectra of 2,5-di-(fluoroalkyl)-l,3,4-oxadiazoles were studied and adiabatic and vertical ionization potentials were given <89JGU24il>. 

An SCF MO calculation gives the following energies for the occupied H20 MOs (Section 1.20) la, 2a]t 1 b2, 3av 1 bx —20.56, —1.28, — 0.62, —0.47, -0.40 hartrees, respectively. For the He 1 PES of H20, answer the following questions, (a) Give the band locations, (b) For each band, state whether or not the adiabatic and vertical ionization potentials will coincide, (c) For each band, state whether the vibrational frequencies of the upper state should be less than, about the same as, or greater than those in the lower state. 

The adiabatic and vertical ionization potentials for Lis are very similar, both being approximately 3.95 eV. This results because of the similar geometries for the 82 state of LisCCsv) and the Ai state of Li3" (D3h). It must be noted, however, that the vertical ionization process for the removal of an electron from linear Lis to give linear Lis leads to the higher ionization potential, 4.39 eV. If both Csv and forms are present in an experiment, a complicated threshold dependence for the ionization process will be observed (j4). The results for Lis exemplify that the fluxional nature of a small metal cluster may complicate the experimental determination of electron affinities and ionization potentials. 

Gas-Phase Basicities, Proton Affinities, and Adiabatic and Vertical Ionization Potenhals of Compounds of N, O, P, and S with Various Hybridizations at 25°C ... 

PES work yielded the following adiabatic and vertical ionization potentials for the outer-valence orbitals ... 

Spectra of outer valence electrons were excited by Nel [1 to 3], Hel [3 to 5], Arl [3], and synchrotron [6] radiation, those of inner valence electrons by Hell [2, 4, 7] and synchrotron [6, 8] radiation. For the respective adiabatic and vertical ionization potentials, see p. 149. Intensities for Hel radiation were compared to those for Hell radiation [4] and to those for Penning ionization (by excited He (23S) atoms) [5]. See also a review [9]. 

Vertical excitation energies and harmonic vibrational frequencies at D3h and C2V symmetries, as well as adiabatic and vertical ionization energies of the neutral molecules, are reported. Good to excellent agreement with a multitude of experimental values was found. 

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