Formation and Evolution of H₂C₃O^+• Radical Cations: A Computational and Matrix Isolation Study

Area of Science:

• Physical organic chemistry
• Astrochemistry
• Computational chemistry

Background:

• Isomeric H2C3O+• radical cations are crucial in physical organic chemistry and extraterrestrial environments.
• Understanding their synthesis and transformations is key to advancing these fields.

Purpose of the Study:

• To experimentally synthesize H2C3O+• isomers from the C2H2···CO complex.
• To computationally investigate the stability and isomerization pathways of H2C3O+• isomers.
• To explore kinetic control in low-temperature chemical reactions.

Main Methods:

• High-level ab initio calculations (UCCSD(T)) for structure, energetics, and properties.
• Fourier-transform infrared (FTIR) spectroscopy in argon matrices at 5 K.
• Electron paramagnetic resonance (EPR) spectroscopy in argon matrices at 5 K.
• Photolysis experiments at specific wavelengths (410-465 nm).

Main Results:

• The ionized C2H2···CO complex transforms into the E-HCCHCO+• isomer under experimental conditions.
• This isomer acts as a key intermediate, demonstrating kinetic control in low-temperature chemistry.
• Photolysis induces transformation to the thermodynamically stable H2CCCO+• isomer.

Conclusions:

• A novel synthetic route to H2C3O+• radical cations was established.
• The study provides evidence for kinetic control in low-temperature chemical reactions.
• The findings have implications for synthesizing highly reactive organic radical cations.