Photodissociation Dynamics of the Zn ⁺ (Acetylene) and Zn ⁺ (Ethylene) Cation-π Complexes

High Resolution Image Download MS PowerPoint Slide Zn + (acetylene) and Zn + (ethylene) ion–molecule complexes are investigated in the gas phase with selected-ion photofragment imaging. UV photodissociation produces respectively Zn + and C 2 H 2 + or Zn + and C 2 H 4 + fragment channels, revealing both simple bond cleavage and charge-transfer dissociation in these complexes. Imaging of each fragment channel reveals considerable kinetic energy release (KER), which provides upper limits on the bond dissociation energies (BDEs): D 0 ≤ 1.04 ± 0.20 eV (24.0 ± 4.6 kcal/mol) for Zn + -(C 2 H 2 ) and D 0 ≤ 0.82 ± 0.18 eV (18.9 ± 4.2 kcal/mol) for Zn + -(C 2 H 4 ). Agreement with previous data from spectroscopic measurements on Zn + (C 2 H 4 ) suggest that these upper limits are near the true BDE for each of these complexes. Density functional theory (DFT) calculations explore the bonding and structures of the Zn + (C 2 H 2 ) and Zn + (C 2 H 4 ) ions, employing the B3LYP, M06, M06-L, and MN15-L functionals. Time-dependent DFT (TD-DFT) computations at the B3LYP/def2-QZVP level characterize the excited states of these complexes. Zn + (C 2 H 2 ) dissociates via absorption to the bound 2 B 2 excited state followed by curve crossing to the 2 A 1 charge-transfer excited state, whereas Zn + (C 2 H 4 ) dissociates via direct excitation of the charge-transfer state.