The Spectroscopy of C₂: A Cosmic Beacon

Area of Science:

• Molecular Spectroscopy
• Astrophysical Chemistry
• Quantum Chemistry

Background:

• Dicarbon (C2) is an abundant interstellar molecule with rich spectroscopy, crucial for understanding astrophysical environments.
• Previous models of C2 photophysics lacked key electronic states and photodissociation processes.
• The unique spectral signature of C2 makes it a sensitive probe of its local environment.

Purpose of the Study:

• To develop more rigorous models of C2 photophysics by identifying previously unobserved electronic states.
• To elucidate the photodissociation pathways of C2, a critical process for its abundance in space.
• To improve the understanding of C2's role in astronomical objects.

Main Methods:

• High-resolution ultraviolet spectroscopy to disentangle complex C2 spectra.
• Computational modeling to characterize electronic states and transition probabilities.
• Analysis of intercombination transitions and predissociation pathways.

Main Results:

• Identification of the c3Σ+ state and associated "Duck" band system (d3Π-c3Σ+).
• Discovery of two new band systems, revealing the 43Π and 33Π states.
• First observation of predissociation in the e3Π state, linked to non-adiabatic coupling with the d3Π state.

Conclusions:

• The study provides the first laboratory evidence for C2 predissociation, explaining its presence in cometary comae but not tails.
• Newly identified states and improved understanding of transitions allow for more accurate astrophysical models of C2.
• This work significantly advances the spectroscopic and photophysical understanding of the dicarbon molecule.