Disentangling the complex spectrum of the ethynyl cation

Area of Science:

• Theoretical Chemistry
• Astrophysical Chemistry
• Physical Chemistry

Background:

• The ethynyl cation (C2H+) is crucial in interstellar chemistry and combustion processes.
• It participates in the synthesis and degradation pathways of organic molecules.

Purpose of the Study:

• Investigate the low-lying electronic states of the ethynyl cation (C2H+).
• Analyze potential energy surfaces and electronic state interactions.
• Determine the adiabatic ionization energy of the ethynyl radical.

Main Methods:

• Utilized pure ab initio computational methodologies.
• Examined potential energy surfaces along stretching and bending coordinates.
• Analyzed electronic state density and wavefunction mixing.

Main Results:

• Identified a high density of electronic states leading to significant interactions.
• Characterized the ground state as 3Π symmetry and the lowest singlet state (1Π) as a Renner-Teller system.
• Calculated the adiabatic ionization energy of the ethynyl radical, matching experimental data.

Conclusions:

• The ethynyl cation exhibits complex electronic behavior due to multiple couplings (Renner-Teller, vibronic, spin-orbit).
• Accurate spectral predictions require accounting for these intricate interactions.
• Despite its small size, C2H+ remains a computationally demanding system.