Phase shift Photoelectron spectroscopy

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. 

An Arrhenius plot of the deposition rate vs reciprocal absolute temperature is shown in Fig. 2. Depositions were made by indicated pressures with or without carrier gas. One notices in all cases that above 190 °C the deposition rate of several A/s was found with an activation energy of about 50-60 kJ mol". Below this temperature a strong decrease of the deposition rate was found. It did not matter whether the gas phase consisted of pure precursor or of a mixture of organometallic compound and argon carrier gas. Only the value of the deposition rate was varying with the different pressures which can be explained by the amount of precursor in the gas phase. Similar results (Fig. 3) were also obtained with in situ X-ray photoelectron spectroscopy (ESCA) studies, which indicate a sharp shift of the binding energy as an onset of the start of decomposition of the precusor at around 190 °C. 

Gas-phase photoelectron spectroscopy has been used to study the bonding in CpM(CO)4, Cp M(CO)4, and (rj -C5H4COMe)Nb(CO)4. The character of two overlapping ionizations in the lowest ionization energy region is dominated by the carbonyls rather than by the metals. The second group of ionizations corresponds to orbitals with predominantly cyclopentadienyl n character that donate to empty metal d orbitals. A much larger shift of these ionizations is observed upon cyclopentadienyl substitution. ... 

In the following it will be reported on a straightforward method to provide information about the dipole matrix elements and phase shifts being essential for the theoretical description of the photoemission process in a relatively simple way and with a pronounced accuracy [2]. This can be achieved by means of photoelectron spectroscopy with linearly polarized light using the ability of a continuous rotation of the electric field vector. The method is exemplarily demonstrated at the system hydrogen on Gd(0001)/W(l 10) which possesses a pronounced adsorbate induced state. 

The discussion above describes the events of electron-molecule interaction in the gas phase. However, in condensed aqueous media, the nature of these processes is significantly altered. For example, dipole-bound states are not likely to be present as they are suppressed by the surrounding medium, and this is confirmed from the photoelectron spectroscopy of the hydrated uracil, thymine, cytosine, and adenine (Schiedt et al. 1998 Eustis et al. 2007) as the photoelectron spectra are blue-shifted with the increase of the number of hydrated water molecules and show valence-bound anion formation. For a visual inspection of this phenomenon, we plotted the LUMO and SOMO surfaces of guanine in neutral and anion radical states, using the B3LYP/6-311++G(2d,p) method in gas phase, and in aqueous media using polarized continuum model (PCM). The LUMO and SOMO siufaces in the gas phase and in the solvated phase of guanine in neutral and in anion radical states are shown in O Fig. 34-10. From O Fig. 34-10, it is inferred that LUMO and SOMO represent a dipole-bound state (Li et al. 2002) in the gas phase (see O Fig. 34-lOa, c), which is destabilized imder the influence of the full solvation and becomes the valence bound state (see O Fig. 34-lOb, d). 

The thermal decomposition of 2-azidoacetic acid (N3CH2CO2H) in the vapour phase has been shown, by photoelectron and matrix isolation infrared spectroscopy, to involve simultaneous formation of CO2 and methanimine (CH2NH) with concerted ejection of N2.52 No evidence was found for formation of intermediate nitrene (NCH2CO2H) or the imine (HNCHCO2H) to which it could be converted by 1,2-hydrogen shift. 

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