The dissociation dynamics and thermochemistry of the acrolein ion studied by threshold photoelectron–photoion coincidence spectroscopy

Abstract

Threshold photoelectron–photoion coincidence spectroscopy has been used to investigate the dissociation dynamics of the acrolein ion (CH 2CHCHO +). The two lowest energy dissociation channels to C 2H 4 ++CO and C 3H 3O ++H are observed at photon energies between 10.0 and 12.0 eV. The C 2H 4 + ion time-of-flight distributions exhibit characteristics of a two-component reaction rate. A three-well-two-channel model is proposed to explain the multi-component dissociation rate. The simulation that fits both the time-of-flight distributions and the breakdown diagram shows that the slow component of the reaction rate for C 2H 4 + production is dominantly caused by tunneling through the isomerization barrier connecting the acrolein ion (A) and the distonic ion, CH 2CH 2CO + (B). After being produced, only small amounts of B isomerize to the lowest energy conformer, the methylketene ion (C). The energy barrier heights of the isomerization from A to B and the C 3H 3O + ion production are 0.87±0.02 and 0.92±0.02 eV, respectively. The 0 K appearance energy of the C 3H 3O + ion is determined to be 11.03±0.02 eV. Using the acrolein heat of formation of −69±10 kJ/mol, the 298 K heat of formation of the CH 2CHCO + ion is determined to be 783±10 kJ/mol.