Photoabsorption spectrum of helium trimer cation--theoretical modeling

Area of Science:

• Physical Chemistry
• Quantum Chemistry
• Atomic and Molecular Physics

Background:

• The photoabsorption spectrum of small helium clusters like He3(+) provides insights into their electronic structure and interatomic interactions.
• Experimental data for He3(+) photoabsorption is limited, particularly in the far UV range.

Purpose of the Study:

• To calculate and analyze the photoabsorption spectrum of He3(+) using two distinct semiempirical models.
• To compare theoretical calculations with existing experimental data and investigate nuclear delocalization effects.
• To predict the far UV absorption spectrum of He3(+) where experimental data is lacking.

Main Methods:

• Semiempirical calculations of intracluster interactions for He3(+).
• Investigation of nuclear delocalization using quantum (exact and harmonic wavefunctions) and classical (Monte Carlo) sampling methods.
• Comparison of calculated spectra with experimental data and predictions for He2(+) photoabsorption.

Main Results:

• The Knowles et al. model showed good agreement with experimental middle UV data for He3(+).
• The Calvo et al. model exhibited significant deviations from experimental results.
• A simple semiempirical point-charge approximation proved effective for calculating transition probabilities in He3(+).

Conclusions:

• The Knowles et al. model is a reliable approach for describing He3(+) photoabsorption spectra.
• Further theoretical and experimental studies are needed to fully characterize the He3(+) photoabsorption spectrum, especially in the far UV region.
• The study validates the use of semiempirical methods and specific approximations for studying small helium cluster ions.