Potential energy distribution, PED

TABLE 9. Theoretical assignments of the vibrational modes of phenol". Potential energy distribution (PED) elements are given in parentheses, frequencies in cm , IR intensities in kmmoG "... 

Another convenient method of characterizing a normal mode is by the potential energy distribution (PED), which describes the relative contributions of various displacement coordinates to the total change in potential energy during the vibration. From Eq. (16) we see that when only one normal mode Qo is excited, the potential energy Va of the molecule is given by... 

The c-vectors" are implicitly used when expressing normal vibrational modes in terms of internal coordinates or when applying the potential energy distribution (PED) analysis to describe vibrational modes [25-27]. However, they have never been used explicitly to define internal modes of a molecule in the sense of Eq. (22). Since c-vectors are associated with internal coordinates qn, and each of the latter describes a molecular fragment internal modes. However, it has been shown that v = Cn is not a satisfactory choice of an internal vibration [19]. 

Table 14.2. Some Relevant Observed and Calculated Frequencies and Approximate Potential Energy Distribution (PED) for the Normal Modes of Hexaazacyclophane...

In the past, in order to describe the normal modes much use has been made of the so-called potential energy distribution (PED). Torkington [31] has first proposed and Morino and Kuchitsu [32] have later generalized the concept of PED defined... 

Hence, for a normal mode of frequency V, one has for the general case where no defined assignment has been given a mixing of the symmetry coordinates which can be "measured" by various methods (e.g., PED = potential energy distribution). 

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