Electron affinity photoelectron spectroscopy

Rienstra-Kiracole JC, Tschumper GS, Schaefer HF et al (2002) Atomic and molecular electron affinities photoelectron experiments and theoretical computations. Chem Rev 102 231-282 liu S-R, Zhai H-J, Castro M, Wang L-S (2003) Photoelectron spectroscopy of Tin- clusters (n = 1-130). J Chem Phys 118 2108-2115... 

In negative ion photoelectron spectroscopy (NIPES), the reactant is a negative ion, and the upper state is neutral. In this case, the origin can be used to determine the electron affinity. 

The ionization potential of a molecule is the energy from the ground state of the molecule (HOMO) to the vacuum level. It is measured using UPS or XPS. The electron affinity of the molecule is the energy from the vacuum level to the LUMO. It is measured using inverse photoelectron spectroscopy (IPES) [15]. The values obtained in the gas phase are different from those obtained in the solid state, and shifts due to amorphous versus crystalline regions can be noticed. 

The theoretical interest in the LiH has increased since the electron affinity of LiH and its deuterated counterpart, LiD, were measured with the use of the photoelectron spectroscopy by Bowen and co-workers [126]. The adiabatic electron affinities of LiH and LiD determined in that experiment were 0.342 0.012 eV for the former and 0.337 0.012 eV for the latter system. The appearance of these data posed a challenge for theory to reproduce those values in rigorous calculations based on the first principles. Since the two systems are small, it has been particularly interesting to see if the experimental EAs can be reproduced in calculations where the BO approximation is not assumed [123]. 

The ethynyl anion provides an example of an sp hybridized carbanion. The high degree of s character in the lone-pair orbital leads to a very large electron affinity for the ethynyl group. Photoelectron spectroscopy indicates an electron binding energy of nearly 70 kcal/mol for the HC=C anion. ... 

A very useful thermodynamic cycle links three important physical properties homolytic bond dissociation energies (BDE), electron affinities (EA), and acidities. It has been used in the gas phase and solution to determine, sometimes with high accuracy, carbon acidities (Scheme 3.6). " For example, the BDE of methane has been established as 104.9 0.1 kcahmol " " and the EA of the methyl radical, 1.8 0.7 kcal/mol, has been determined with high accuracy by photoelectron spectroscopy (PES) on the methyl anion (i.e., electron binding energy measurements). Of course, the ionization potential of the hydrogen atom is well established, 313.6 kcal/ mol, and as a result, a gas-phase acidity (A//acid) of 416.7 0.7 kcal/mol has been... 

We have already shown that excitation energies can be diagrammatically decomposed to yield simpler quantities such as ionization potentials and electron affinities plus some remaining diagrams. MB-RSPT permits the use of this treatment for even more complex processes. In this section, we present the applicability of the theory to double ionizations observed in Auger spectra as well as excitations accompanying photoionization (shake-up processes) observed in ESCA and photoelectron spectroscopy. A detailed description of this approach is given in Refs.135,136. Here we shall present only the formal description. 

Electron affinities can be determined with even higher accuracy by photoelectron spectroscopy of negative ions. This technique has been used to determine the electron affinity... 

Ab initio molecular orbital calculations were reported for methylenes CXY, methyli-dynes CX and for their anions, CXY- and CX-, where X and Y are all possible combinations of H, F and Cl325. Gas-phase acidities, electron affinities and heats of formation have been calculated325. CXY- anions (X = F, Cl, Br and I, Y = H) have also been studied by photoelectron spectroscopy and structures have been reported327. 

The electron affinity can also be deduced from the measurement of the spectrum of the photoelectron emission with monochromatic UV light. This technique is ultra-violet (UV) photoelectron emission spectroscopy (or UV photoemission spectroscopy or UPS). The UPS technique involves directing monochromatic UV light to the sample to excite electrons from the valence band into the conduction band of the semiconductor. Since the process occurs near the surface, electrons excited above the vacuum level can be emitted into vacuum. The energy analysis of the photoemitted electrons is the photoemission spectrum. The process is often described in terms of a three step model [8], The first step is the photoexcitation of the valence band electrons into the conduction band, the second step is the transmission to the surface and the third step is the electron emission at the surface. The technique of UPS is probably most often employed to examine the electronic states near the valence band minimum. 

Wang XB, Woo HK, Wang LS, Minofar B, Jungwirth P (2006) Determination of the electron affinity of the acetyloxyl radical (CH3COO) by low-temperature anion photoelectron spectroscopy and ab initio calculations. Journal of Physical Chemistry A 110 5047-5050. 

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