Electron adiabatic detachment energy

Adiabatic detachment energy [7]. Abbreviations used rcoy (Em) = covalent radius of element E in a trivalent compound BE(E-E) = bond enthalpy of a single E-E bond D°298(E2) = dissociation enthalpy of the E2 molecule at standard conditions IE = ionization enthalpy EA = electron affinity AHf°(E2 g) = standard enthalpy of formation of the gaseous E2 molecule. 

Table 21-1. Values of stabilization energy (Estab), stabilization free energy (Gslab), their relative values (AE and AG calculated with respect to the Watson-Crickpair), electron vertical detachment energy (VDE) and adiabatic electron binding energy (EBE0) for the anionic adenine-thymine and 9-methyladenine-1-methylthymine complexes calculated at the B3LYP/6-31+G level. (Table 1 of ref. [49]. Reprinted with permission. Copyright 2005 American Chemical Society.)...

Table 21-2. Relative electronic energies and free energies (AE and AG) calculated with respect to the aHX(AT) or aHX(AT)-SPT anion together with the adiabatic electron affinities (AEAG) and electron vertical detachment energies (VDE) for the anionic HX(AT) complexes predicted at the B3LYP/6-31+G" level. AE and AG in kcal/mol AEAG and VDE in eV...

ADE = adiabatic detachment energies ESC A = electron spectroscopy for chemical analysis HOMO = highest occupied molecular orbitals MAES = metastable atom electron spectroscopy MIES = metastable ionization electron spectroscopy OAT = oxygen atom transfer PES = photoelectron spectra PEI = pulsed field ionization PIES = Penning ionization electron spectroscopy QM = quantum-mechanical REMPI = resonantly enhanced multiphoton ionization SC = semiclassical VDE = vertical detachment energies XPS = x-ray photoelectron spectroscopy ZEKE = zero electron kinetic energy Cp = cyclopentadienyl, Ph = phenyl, CeHs Tp =... 

Anion photoelectron spectroscopy [37, 38] amd photodetachment techniques [39] provide accurate information on electron detachment energies of negative ions. Ten closed-shell ainions considered here exhibit sharp peaks, indicative of minor or vanishing final-state nuclear rearrangements, in their photoelectron spectra. Comparisons between theory and experiment are straiightforward, for differences between vertical and adiabatic electron detachment energies (VEDEs and AEDEs, respectively) are small. 

Figure 20-3. Electron binding energies for molecule M in anionic state are defined pictorially in a representation of the potential energy surfaces of the neutral molecule (M) and anion radical (M ) with the lowest vibration energy level shown for each. During a vertical process, the geometry remains unchanged but for the adiabatic process structural relaxation occurs. Thus the VDE (vertical detachment energy) and VEA (vertical electron affinity) represent the upper and lower bounds to the adiabatic electron affinity (AEA)...

The adiabatic electron detachment energies of all 16 possible monoanionic dinucleotides have been tabulated in [50], but no VDE values were reported. The spectra of a few dinucleotides were displayed in the same publication. These included the spectra of dAA, dCC-, dGG-, dTT, dAG, dCG, dGA-, and dTG-. With some careful inspection of the onsets, it is possible to estimate VDEs from these spectra. 

As an illustration consider C=C=C=C which is a triplet ( Sg ) with a -It HOMO occupied by two electrons of parallel spin. Table 21 displays results obtained with several different levels of correlation and basis sets." There are actually three different quantities that can be computed the vertical electron detachment energy (VEDE, energy to eject electron at the geometry of the anion) the adiabatic electron affinity (AEA, when the neutral M is allowed to relax to its optimum geometry), and the vertical electron affinity (VEA, where the geometry of the neutral is assumed for the anion). 

Figure 43. The upper panel shows adiabatic potential energy curves Vn(R) for several electronic states. The +) state is obtained if the single electron is detached from the system. Dipole matrix elements are shown in the lower panel of the figure.

TTie vertical electron detachment energy (VDE) is calculated as the total energy difference between the anionic and neutral clusters, both taken in the anionic optimized geometry without die ZPVE. The adiabatic electron affinity (EAa) and ionization energy (lEa) are calculated as the total energy difference between the anionic and cationic clusters, respectively, and the parent neutral cluster in their optimized geometries. 

Two experimental results are available for the adiabatic electron affinity which were obtained by photodetachment studies on PH ions. A=1.028 0.010 eV was obtained from a laser (488 nm) photoelectron spectrum of PH after rotational corrections had been made to the detachment energy measured from the center of the PH(X v=0) PH (X rij, v = 0) peak [1]. A less precise result, A=1.00 0.06 eV, has been obtained from the lowest threshold energy of the photodetachment cross section measured between 0.8 and 2.8 eV (1.5 to 0.4 xm a second threshold at -1.9 eV obviously corresponds to the PH(a A) PH (X rij) transition) [2]. 

Potential energy surfaces (PES) of an anion formation (M ) after electron (e ) attachment to the neutral molecule (M). When the energy of an anion (M ) lies below the neutral molecule, positive electron affinity Is observed [left) otherwise the molecule is said to have negative electron affinity right). Energy changes shown for an electron attachment or detachment event are (1) the vertical electron affinity (VEA), (2) the adiabatic electron affinity (AEA), and (3) the vertical detachment energy (VDE). The VDE and VEA impose the upper and lower bounds to AEA... 

Note that Eq. [2] defines the VDE, which excludes relaxation of the neutral species following electron detachment. Including that relaxation energy defines the adiabatic electron detachment energy, which is more often called the adiabatic electron affinity (AEA),... 

Figure 16 Schematic view of Sq -> Sj excitation in p-coumaric acid in its phenolate (a) or carboxylate (b) isomeric form. (Energies are given in electron volts.) In either case, the Sj state lies above the anion s adiabatic detachment threshold and is thus embedded in a continuum of electron-detached states. The core-excited rrrc resonance may be classified as a shape resonance (on the left) or a Feshbach resonance (on the right) depending on whether the low-lying continuum corresponds to detachment from the ir system (a" orbital) or from an a orbital that is not involved in the jr ir excitation. Adapted with permission from Ref. 186 copyright 2013 American Institute of Physics.

We calculate the enthalpy of formation at 0 K as the difference between a H"(PF, g, OK) = -8.55 5.0 kcal mol" (1 ) and the selected value of 1.1 0.5 eV (25.366 kcal mol" ) for the electron affinity (EA) of PF. The value of EA refers to the vertical electron detachment process PF"(g) = PF(g) + e" and is taken from the molecular orbital study of O Hare 2). This value was obtained from Hartree-Fock energies and estimated corrections for correlation effects. The estimated uncertainty in EA is 0.5 eV which should be adequate to cover the possibility that the adiabatic value is lower than the vertical EA. Other theoretical predictions of EA include 2.55 eV ( ) and 1.4 eV (4). 

The behavior of CTTS states is dependent on energy levels of the ion-solvent molecular couphngs. These levels can lead to internal relaxation and/or complete electron detachment via adiabatic or nonadiabatic electron transfer. The ultrafast spectroscopic investigations of electronic dynamics in ionic solutions would permit us to learn more about the primary steps of an electron-transfer reaction within a cationic atmosphere. The influence of counterions on early electron photodetachment trajectories from a hahde ion can be considered as prereactive steps of an electron transfer. 

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