Electronic spectroscopy of C2 in solid rare gas matrixes

Area of Science:

• Physical Chemistry
• Spectroscopy
• Computational Chemistry

Background:

• The electronic spectroscopy of diatomic molecules in rare gas matrices provides insights into molecular interactions and electronic transitions.
• Previous studies on C(2) in rare gas matrices have established characteristic absorption bands, but matrix-specific effects, especially in heavier noble gases, require further investigation.

Purpose of the Study:

• To investigate the electronic spectroscopy of the C(2) molecule isolated in argon (Ar), krypton (Kr), and xenon (Xe) matrices.
• To characterize new absorption bands observed in Kr and Xe matrices and elucidate their origins, including charge-transfer phenomena and the formation of new species.
• To complement experimental spectroscopic data with high-level electronic structure calculations to aid in spectral assignments and understand the C(2)-rare gas interactions.

Main Methods:

• Electronic spectroscopy was performed on C(2) molecules embedded in Ar, Kr, and Xe matrices over the 150-500 nm wavelength range.
• High-level electronic structure calculations, including Multi-Configurational Self-Consistent Field (MCSCF) and Coupled-Cluster methods (CCSD(T), BCCD(T)), were employed.
• Correlation-consistent basis sets were utilized in the computational studies to ensure accuracy in predicting electronic properties and molecular structures.

Main Results:

• In Ar matrices, the D ((1)Sigma(u)(+)) <-- X ((1)Sigma(g)(+)) Mulliken band was observed as the sole UV absorption.
• In Kr matrices, additional bands were assigned to Kr(n)()(+)C(2)(-) <-- Kr(n)()C(2) charge-transfer absorptions.
• In Xe matrices, the Mulliken band was absent, and new bands appeared near 300 nm and 423 nm, with the latter assigned to the forbidden B'((1)Sigma(g)(+)) <-- X ((1)Sigma(g)(+)) transition, suggesting the formation of a bound C(2)Xe species. Computational studies predicted a linear ground-state structure for C(2)Xe with significant multireference character, contradicting prior DFT studies.

Conclusions:

• The electronic spectral behavior of C(2) is significantly influenced by the surrounding rare gas matrix, particularly in heavier noble gases like Xe.
• The formation of a bound C(2)Xe species leads to distinct spectral features, including the absence of the Mulliken band and the appearance of new transitions.
• Advanced computational methods provide crucial support for interpreting experimental spectra and understanding the electronic structure and bonding in C(2)-rare gas systems.