UV absorption spectrum of allene radical cations in solid argon

Area of Science:

• Physical Chemistry
• Spectroscopy
• Quantum Chemistry

Background:

• Matrix isolation spectroscopy is crucial for studying unstable molecular species.
• Understanding the electronic structure of small organic cations provides insights into reaction mechanisms.
• Previous work identified allene and propyne cations via infrared spectroscopy.

Purpose of the Study:

• To characterize the ultraviolet absorption spectrum of allene cations in solid argon.
• To assign observed electronic transitions based on experimental and computational data.
• To investigate the photolytic behavior of allene cations.

Main Methods:

• Argon matrix isolation with electron bombardment deposition.
• Infrared (IR) and ultraviolet (UV) absorption spectroscopy.
• Photolysis experiments and time-dependent density functional theory (TD-DFT) calculations.

Main Results:

• Allene cations were generated in solid argon via electron bombardment.
• UV absorption spectrum revealed two electronic transitions: A 2E ← X 2E (266-237 nm) and B 2A1 ← X 2E (229-214 nm).
• Observed spectral features and photolytic behavior align with TD-DFT calculated excitation energies and oscillator strengths.

Conclusions:

• The electronic transitions of allene cations in solid argon have been assigned.
• The study validates the use of UV-Vis spectroscopy combined with computational methods for characterizing molecular cations.
• The findings contribute to the understanding of the spectroscopy and photochemistry of small hydrocarbon ions.