Velocity map imaging apparatus applicable to a study of multiple photofragmentation of C60

A velocity map imaging (VMI) spectrometer was constructed for observation of the slow ions produced by photofragmentation of C60 with synchrotron radiation. The spectrometer was tested by observing the ion images of rare gases in the Maxwell–Boltzmann distribution at room temperature, and the effect of a large ionization volume inevitable in our experiment has been quantitatively characterized. Numerical simulations taking into account such instrumental parameters indicate that one can distinguish the two independent formation processes of C 56 + from the primary precursor C 60 + : i.e., one-step ejection of C4 and sequential ejections of two C2 fragments.