Shapes of fall-off curves

2 I say principally because there may be other reasons for the flattening that occurs between the 3-atom and the 6-atom case, see Chapter 8. 

3 A major stumbling block for RRK theory has been that it is often not possible to find a unique value of the Kassel parameter s which will give both the correct shape of the fall-off curve and the correct position on the pressure axis [72.S2] the reason for this has been analysed recently [82.S1], 

Notice also that different isotopic variants of the same molecule exhibit small but measurable differences in fall-off behaviour these differences are not easily described within as simple a framework as is represented by equation (1.7). 

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Little needs to be added here concerning the shapes of fall-off curves. For the strong collision case, it was shown in Chapter 5 how such shapes... 

On the experimental front, by the early 1960s, thermal reactions exhibiting fall-off with pressure were no longer a rarity, but I could not see at that time how further study of the shapes of fall-off curves would be helpful on the theoretical front so I started to look for other useful experiments. I thought that if we could react methyl radicals with trichloromethyl radicals at various pressures, we might be able to probe the k(E) function for the elimination of HQ from the vibrationally excited methylchloroform intermediates which would be formed, i.e. 

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