6.3.2 Sequential Simple Cleavages

Sequential (secondary) simple cleavages may also occur. For example, the fragment AB$^{\textrm{+}}$ (produced by reaction (1) in Section 6.3.1) may continue to decompose:

AB$^{\textrm{+}}$ $\rightarrow$ A$^{\textrm{+}}$ + B$^{\textrm{.}}$ (7)

AB$^{\textrm{+}}$ $\rightarrow$ A$^{\textrm{.}}$ + B$^{\textrm{+}}$ (8)

Notice that there are two ways to form an ion at the nominal mass of A (reaction (3) in one step and sequential reactions (1) followed by (7)), and two ways to form an ion at the mass of B. We have proposed two mechanisms for the formation of both A and B ions: a one-step mechanism and a two-step mechanism. The two mechanisms will probably have different kinetics; one or both pathways to A, for example, may be 'unfavorable.'

The multiplicity of A formed by the two different mechanisms is different. The A ion formed by reaction (3) is most likely in a singlet state, whereas formation of the A ion formed by reaction (1) then reaction (7) is most likely in a doublet state. The structures of these two product ions will therefore possibly be different, though they lie at the same mass.