Imaging the dissociation dynamics of Si₂⁺ via two-photon excitation at 193 nm^†

In the one-color experiment at 193 nm, we studied the photodissociation of Si₂⁺ ions prepared by two-photon ionization using the time-sliced ion velocity map imaging method. The Si⁺ imaging study shows that Si₂⁺ dissociation results in two distinct channels: Si(³P_g)+Si⁺(²P_u) and Si(¹D₂)+Si⁺(²P_u). The main channel Si(³P_g)+Si⁺(²P_u) is produced by the dissociation of the Si₂⁺ ions in more than one energetically available excited electronic state, which are from the ionization of Si₂(v=0−5). Particularly, the dissociation from the vibrationally excited Si₂(v=1) shows the strongest signal. In contrast, the minor Si(¹D₂)+Si⁺(²P_u) channel is due to an avoided crossing between the two ²Π_g states in the same symmetry. It has also been observed the one-photon dissociation of Si₂⁺$(X4Σg−)$ into Si(¹D₂)+Si⁺(²P_u) products with a large kinetic energy release.