Direct IR Absorption Spectra of Propargyl Cation Isolated in Solid Argon

Area of Science:

• Physical Chemistry
• Spectroscopy
• Quantum Chemistry

Background:

• Propargyl cations are key intermediates in various chemical reactions.
• Understanding their vibrational properties is crucial for reaction mechanism elucidation.
• Previous spectroscopic data on these cations were limited.

Purpose of the Study:

• To directly record the infrared (IR) absorption spectra of propargyl cations.
• To assign the observed vibrational bands using complementary experimental and theoretical data.
• To characterize the vibrational modes, including the previously unreported ν11 mode.

Main Methods:

• Generation of propargyl cations via electron bombardment of propyne in an Argon matrix.
• Matrix isolation spectroscopy for recording IR absorption spectra.
• Secondary photolysis with UV light to differentiate product bands.
• Comparison with infrared photodissociation (IRPD), velocity-map imaging photoelectron (VMI-PE) data, and theoretical predictions.

Main Results:

• Direct IR absorption spectra of propargyl cations were successfully obtained.
• Most IR-active bands with observable intensity were assigned.
• The ν11 vibrational mode of the propargyl cation was reported for the first time.
• Deuterium-substituted isotopic ratios supported the band assignments.

Conclusions:

• This study provides a comprehensive IR spectral characterization of the propargyl cation.
• The identification of the ν11 mode advances the understanding of propargyl cation vibrational dynamics.
• The combined experimental and theoretical approach validates the spectral assignments.