Four-body-fragmentation dynamics of acetylene by highly-charged-ion impact

The four-body fragmentation of acetylene molecular ions (C2Hq+2 , 4 q 8) upon impact with 1 MeV Ar8+ projectile ions with C2H2 molecules, using cold target recoil ion momentum spectrometer (COLTRIMS), is studied by measuring momenta of fragments in a recoil-ion projectile-ion coincidence measurement. Chargesymmetric (-asymmetric) channels in which carbon ions share the same (different) charge are observed. Within the fragmentation of a parent ion, where there is a possibility of both the symmetric and asymmetric charge distribution of carbon ion, charge-symmetric breakup channels are favored over charge-asymmetric ones. Kinetic energy release (KER) distributions are presented and probable electronic states are associated with particular features in the KER distribution by using high-level ab initio quantum chemical calculations. The ab initio calculations also indicated that the difference between KER values for linear and bent structures (cis- and trans-configurations) is of the order of 0.1 eV. The projectile's final charge state after the collision and the reaction windows calculation within the framework of the extended classical overbarrier model examine the role of various electron-capture-associated processes in the formation of the molecular ions in a particular charge state. We observed that as the acetylene ion's charge state increases, the contribution from capture stabilization also increases, indicating the population of captured electrons into the lower energy states of the projectile. The momentum correlation plots in fragments' momentum space were used to visualize the fragmentation mechanism, and the observation of the double distribution of momenta of carbon ions for charge-asymmetric channels showed the direct signatures of fragmentation from two different molecular orientations with respect to the spectrometer axis.