Valence Threshold Photoionization Spectra of C 5 $_5$ H and C 5 $_5$ H 2 $_2$ Isomers

Area of Science:

• Physical Chemistry
• Chemical Physics
• Spectroscopy

Background:

• C5Hx species are vital intermediates in the synthesis of complex carbonaceous molecules.
• Understanding their structure is key to modeling combustion processes and interstellar chemistry.

Purpose of the Study:

• To record and assign mass-selected threshold photoelectron spectra (TPES) for linear and cyclic C5Hx isomers.
• To establish reliable methods for distinguishing between different C5Hx isomers using high-resolution spectroscopy.
• To provide benchmarks for identifying these reactive intermediates in various chemical environments.

Main Methods:

• Double-imaging photoelectron-photoion coincidence spectroscopy was employed to obtain TPES.
• Transient C5Hx species were generated in situ via hydrogen abstraction reactions using fluorine atoms in a discharge flow-tube reactor.
• Ab initio calculations and Franck-Condon simulations were used for spectral assignment and ionization energy determination.

Main Results:

• TPES for l-C5H and c-C3H-CCH were reported for the first time.
• Accurate adiabatic ionization energies were determined for the studied C5Hx isomers.
• The study demonstrated that high-resolution TPES effectively distinguishes between linear and cyclic C5Hx isomers, surpassing photoion yield methods.

Conclusions:

• The developed TPES method provides a robust fingerprint for identifying C5Hx isomers.
• These findings offer critical data for understanding hydrocarbon formation in combustion and astrochemical settings.
• Similar isomeric distributions were observed from distinct precursors, suggesting common formation pathways.