Probing the barrier for CH2CHCO --> CH2CH + CO by the velocity map imaging method

Area of Science:

• Chemical Kinetics and Dynamics
• Photochemistry
• Spectroscopy

Background:

• Understanding radical dissociation is crucial for combustion and atmospheric chemistry.
• The CH2CHCO radical is an important intermediate in various chemical reactions.
• Previous studies have lacked precise experimental determination of its dissociation barrier.

Purpose of the Study:

• To experimentally determine the dissociation barrier height for CH2CHCO --> CH2CH + CO.
• To compare experimental findings with theoretical predictions from various electronic structure methods.
• To assess acryloyl chloride as a photolytic precursor for generating CH2CHCO radicals.

Main Methods:

• Two-dimensional product velocity map imaging was employed to study the dissociation.
• CH2CHCO radicals were generated via C-Cl bond fission in acryloyl chloride photodissociation at 235 nm.
• State-selective detection of Cl atoms and non-dissociated radicals using resonance-enhanced multiphoton ionization.

Main Results:

• The experimentally determined dissociation barrier for CH2CHC*O --> CH2CH + CO is 21+/-2 kcal mol(-1).
• The corresponding barrier for C*H2CHCO --> CH2CH + CO was determined to be 23+/-2 kcal mol(-1).
• Coupled-cluster and Gaussian-3 methods accurately predicted the dissociation barriers, while DFT methods underestimated them.

Conclusions:

• The study provides the first experimental determination of the CH2CHCO dissociation barrier.
• Acryloyl chloride serves as an effective photolytic precursor for generating CH2CHCO radicals with controlled internal energies.
• The findings validate advanced computational chemistry methods for predicting reaction dynamics.