Structure of the Se₄ Isomers─An Ab Initio Study

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Astrochemistry

Background:

• Selenium's role in astrophysics remains incompletely understood.
• Experimental data on selenium clusters like Se4 is limited.
• Supernova nucleosynthesis confirms selenium's extraterrestrial origin.

Purpose of the Study:

• To computationally determine the equilibrium geometries of four Se4 isomers.
• To calculate electronic properties including electron affinity and ionization energy.
• To predict electronic transitions relevant to astrophysical observations.

Main Methods:

• Coupled cluster single and double perturbative (CCSD(T)) method with complete basis set extrapolation.
• Multireference configuration interaction (MRCI) method for electronic transitions.
• Analysis of equilibrium geometries, bond lengths, and valence angles.

Main Results:

• The C2v Se4 isomer exhibits a ground-state geometry closely matching theoretical predictions.
• Calculated adiabatic and vertical electron affinities and ionization energies are reported.
• Predicted electronic transition wavelengths align with experimental near-infrared absorption bands (710-850 nm).

Conclusions:

• Theoretical insights into Se4 electronic and geometric structures are provided.
• Spectroscopic data aids in identifying selenium-containing molecules in extraterrestrial environments.
• Findings contribute to understanding selenium's presence and behavior in astrophysical settings.