The time-of-flight (TOF) spectrum for the dissociation of 1,3-butadiene (mass = 54 amu) is shown in figure where several fragments of the kind C n H + m with n = 1 to 4 and m = 0 to 6 are visible. We note that fragments originating from all possible bond cleavages appear in the TOF spectrum. Furthermore, fragments H Some of the fragments recorded in our experiment can only be formed by the process of hydrogen scrambling and/or hydrogen migration like