Excitation Number: Characterizing Multiply Excited States

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Spectroscopy

Background:

• Determining the number of excited electrons in electronic transitions is crucial for understanding molecular behavior.
• Previous methods for quantifying excitation can lead to ambiguous or incorrect assignments.
• Accurate characterization of excited states is vital for predicting molecular properties and reaction pathways.

Purpose of the Study:

• Introduce a novel metric, the excitation number (η), to unambiguously quantify excited electrons.
• Provide a more reliable method for characterizing electronic transitions compared to existing approaches.
• Demonstrate the utility of η in analyzing excited-state properties across various molecular systems.

Main Methods:

• Modeling initial and final electronic states using single-determinant wave functions.
• Developing and applying the excitation number (η) calculation.
• Analyzing several case studies to validate the method's accuracy and applicability.

Main Results:

• Calculated excitation number (η) values consistently approximate positive integers.
• The excitation number (η) provides clear and unambiguous assignments of excited electrons.
• Demonstrated improved excited-state characterizations in various examples compared to prior methods.

Conclusions:

• The excitation number (η) offers a robust and precise way to determine the number of excited electrons.
• This new metric resolves ambiguities inherent in previous excitation quantification methods.
• η facilitates more accurate and reliable characterization of excited electronic states in molecules.