Intersystem crossing and dynamics in O(3P) + C2H4 multichannel reaction: experiment validates theory

Area of Science:

• Chemical Kinetics and Dynamics
• Atmospheric Chemistry
• Combustion Chemistry

Background:

• The O(3P) + C2H4 reaction is a key process in combustion and atmospheric chemistry.
• This reaction involves complex interactions between triplet and singlet potential energy surfaces (PESs) through intersystem crossing (ISC).
• Challenges in studying this reaction arise from high-dimensional PESs and long-lived collision complexes.

Purpose of the Study:

• To experimentally determine primary products and branching ratios (BRs) for the O(3P) + C2H4 reaction at a collision energy of 8.4 kcal/mol.
• To infer the extent of intersystem crossing (ISC) from observed product BRs.
• To theoretically model the reaction dynamics on coupled singlet-triplet PESs and compare with experimental data.

Main Methods:

• Experimental determination of product branching ratios using crossed molecular beam experiments with soft electron-ionization mass-spectrometric detection.
• Theoretical calculations involving a new full-dimensional PES for the triplet state and spin-orbit coupling to the singlet PES.
• Running approximately half a million surface hopping trajectories on the coupled singlet-triplet PESs.

Main Results:

• Five competing reaction channels were identified, yielding products such as H + CH2CHO, CH3 + HCO, and others.
• Experimental and theoretical findings indicate nearly equal contributions from both singlet and triplet PESs to the overall reaction.
• Excellent agreement was observed between experimental and theoretical angular and translational energy distributions for major product channels.

Conclusions:

• The study validates advanced theoretical methods for accurately describing complex, multichannel, nonadiabatic reactions.
• The significant role of intersystem crossing (ISC) in this reaction highlights its importance in combustion chemistry.
• Theory has reached a high level of capability in predicting the dynamics of intricate chemical reactions.