Population analysis energy-resolved

When going over to more than one atom (or atomic orbital) per unit cell, the density-of-states must be analyzed in greater detail the aforementioned Mul-liken population analysis is still needed, but in an energy-resolved form. 

The complementary method to time-resolved measurements is the spectroscopy in the energy domain. Energy-resolved experiments determine the Fourier transform of the exponential decay in the time domain, which yields a Lorentzian for the intrinsic spectral lineshape. As mentioned in Section 3.2.4, photoemission does not permit to separate inelastic and elastic decay processes, which both contribute to the linewidth. Because the energy resolution of inverse photoemission is usually not sufficient for a lineshape analysis, this section is devoted to photoemission of occupied states, providing an additional complementary aspect to the time-resolved measurements of transiently populated unoccupied states by 2-PPF. Occupied (initial) states can also be observed by 2-PPE spectroscopy. Their linewidth is similar to the values obtained in regular photoemission [107]. 

Detailed NMR conformational analysis of y -peptides 139-141 (Fig. 2.35) in pyri-dine-d5 revealed that y-peptides as short as four residues adopt a 2.6-hehcal fold stabilized by H-bonds between C=0 and NH +3 which close 14-membered pseudocycles [200, 201]. The 2.614-helical structure of a low energy conformer of y-hex-apeptide 141 as determined from NMR measurements in pyridine-d5 [200], is shown in Fig. 2.36A and B). Determination of the structure of y" -peptides in CD3OH was hampered by the much lower dispersion of the diasterotopic H-C(a) protons compared to their dispersion in pyridine-d5. However, the characteristic and properly resolved i/ir-2 NOE crosspeacks between H-C(y) and NH +2 in the NH/H-C(y) region of the ROESY spectrum were an indication that the 2.6-helical structure is at least partially populated in CD3OH. 

In an experiment attempting to resolve the identity of the CFj, mixtures of C2F4 and NO2 were flash photolyzed in Pyrex (A >300 nm) to avoid dissociating the C2F4, and the CO product was monitored by the CO laser. The CO was found to be vibrationally excited up to n=ll, corresponding to as much as 63 kcal/mole of energy. By analysis of the observed population distribution and consideration of all possible paths and energetics associated with this reaction, it was concluded that CO excited to this extent could come only from the process ... 

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