High-resolution energy-loss spectroscopy spectra

The geometry of N2 is assigned to side-on based on detailed interpretation of the X-ray photoelectron spectroscopy spectrum [460, 461] and of the high-resolution electron-energy-loss spectroscopy spectrum [470]. 

HREELS High-resolution electron energy-loss spectroscopy [129, 130] Same as EELS Identification of adsorbed species through their vibrational energy spectrum... 

Analytical electron microscopy (AEM) can use several signals from the specimen to analyze volumes of catalyst material about a thousand times smaller than conventional techniques. X-ray emission spectroscopy (XES) is the most quantitative mode of chemical analyse in the AEM and is now also useful as a high resolution elemental mapping technique. Electron energy loss spectroscopy (EELS) vftiile not as well developed for quantitative analysis gives additional chemical information in the fine structure of the elemental absorption edges. EELS avoids the problem of spurious x-rays generated from areas of the spectrum remote from the analysis area. 

As noted in the introduction, vibrations in molecules can be excited by interaction with waves and with particles. In electron energy loss spectroscopy (EELS, sometimes HREELS for high resolution EELS) a beam of monochromatic, low energy electrons falls on the surface, where it excites lattice vibrations of the substrate, molecular vibrations of adsorbed species and even electronic transitions. An energy spectrum of the scattered electrons reveals how much energy the electrons have lost to vibrations, according to the formula ... 

In order to show that the strongly bound species was actually an EpB molecule, high-resolution electron energy loss spectroscopy (HREELS) was used to study the species present at the various dosing temperatures. When dosed at lower temperatures, most of the observed peaks in the HREELS matched those of the vibrational spectrum of liquid EpB, suggesting that intact EpB is interacting with the silver surface at lower temperatures. However, the silver surface dosed with EpB at 300 K showed noticeable differences in the HREELS spectrum. In addition, DPT calculated vibrational frequencies of the surface bound oxaraetallacylce matched well with those determined experimentally. 

The product of the collision-induced dissociative chemisorption event is identified by high resolution electron energy loss spectroscopy. Fig. 9a shows the vibrational spectrum of a monolayer of methane at 46 K before bombardment with Ar. The vibrational frequencies are unperturbed from the gas phase values within the resolution of this technique ( 20 cm-1). The loss observed at 1305 cm" is assigned to the V4 mode, the loss at 1550 cm- to the >2 mode and the losses at 2895 cm 1 and 3015 cm- to the vi and V3 modes, respectively. Fig. 9b shows the vibrational spectrum after exposure of the methane monolayer at 46 K to a beam of Ar atoms with a translational energy of 36 kcal/mole. This spectrum has been assigned previously to an adsorbed methyl radical. 

Figure 1 An overview of high resolution electron energy loss spectroscopy. Top left the incident electron beam is shown as a narrow, intense peak on the intensity vs energy loss axes. The specularly reflected beam is shown with loss peaks due to adsorbed molecules, with modes tuo. Centre The scattering mechanism is illustrated with the three diatomic molecules adsorbed on the sur ce with perpendicular and parallel orientation relative to the sur ce. Mode has a dynamic dipole moment pa which is perpendicular to the sur ce, and induces a second image dipole in the same direction, so that the electron scatters from a combined dipole moment of 2p . This is the dipole scattering process. The mode o>2 is parallel to the surface, and the induced image dipole cancels the molecular dynamic dipole moment. The mode is screened and is not present in the spectrum if there is no impact contribution to the scattering. Mode (03 is shown with the dynamic dipole moment equal to zero (the orientation is not relevant). The mode will be observed as an impact mode.

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