Four-body Coulomb explosion of acetylene in collision with highly charged ions

The dynamics of four-body Coulomb explosion of acetylene in collision with 50 keV/u ${\mathrm{Ne}}^{8+}$ are investigated by detecting all four ionic fragments and the scattered projectile in quintuple coincidence. Six different breakup channels of ${\mathrm{C}}_{2}{{\mathrm{H}}_{2}}^{q+}$ cations with $4\ensuremath{\leqslant}q\ensuremath{\leqslant}8$ are identified. The kinetic energy (KE) distributions of all ionic fragments as well as the total kinetic energy release (KER) distributions are obtained and compared with the calculation results of the point-charge (PC) approximation model for each channel. For symmetric charge distribution channels, the calculations of PC model, in general, agrees well with the peak positions of the measured KER and KE distributions for all three channels with the largest deviation appearing in the breakup of ${\mathrm{C}}_{2}{{\mathrm{H}}_{2}}^{4+}$. However, for asymmetric charge distribution channels, although the KER values calculated by the PC model for the breakup of ${\mathrm{C}}_{2}{\mathrm{H}}_{2}^{5+}$ and ${\mathrm{C}}_{2}{\mathrm{H}}_{2}^{7+}$ fit very well with experiment, the KEs of the two protons and the two C cations exhibit noticeable discrepancy between experiment and PC model. In addition, it is found that the fragmentation of ${\mathrm{C}}_{2}{{\mathrm{H}}_{2}}^{6+}$ which may lead to either two ${\mathrm{C}}^{2+}$ cations or one ${\mathrm{C}}^{+}$ and one ${\mathrm{C}}^{3+}$ cation shows a strong preference for symmetric charge distribution between the two C cations.