Complete, Theoretical Rovibronic Spectral Characterization of the Carbon Monoxide, Water, and Formaldehyde Cations.

Area of Science:

• Computational Chemistry
• Astrophysical Spectroscopy
• Quantum Chemistry

Background:

• Spectroscopic analysis of cometary species is vital for understanding their evolution.
• Excited electronic states of small molecular cations are key targets for cometary spectral analysis.
• Accurate theoretical predictions are needed to interpret complex spectral data.

Purpose of the Study:

• To develop and apply novel high-level ab initio quartic force field (QFF) methods.
• To compute spectroscopic data for electronically excited states of carbon monoxide, water, and formaldehyde cations.
• To provide assignments for vibrational frequencies and rotational constants for these species.

Main Methods:

• Equation-of-motion ionization potential (EOM-IP) coupled cluster methods with complete basis set extrapolation.
• Core correlation corrections and approximate triples coupled cluster methods.
• Equation-of-motion coupled cluster (EOM-CC3) and previous (T)+EOM approaches.

Main Results:

• Assignments for fundamental vibrational frequencies of formaldehyde cation's A˜2B1 and B˜2A1 states.
• First-time provision of rotational constants for excited states of formaldehyde and water cations.
• Support for re-assignment of water cation's B˜2B2 state vibrational frequencies (ν1, ν3).
• High accuracy (within 12 cm-1) for water cation's ground electronic state vibrational frequencies.

Conclusions:

• The developed QFF methods accurately predict spectroscopic properties of molecular cations.
• The computed data will aid in cometary spectral analysis and remote sensing applications.
• This work advances fundamental understanding of molecular spectroscopy for extraterrestrial environments.