Potential-Energy Surfaces, the Born-Oppenheimer Approximations, and the Franck-Condon Principle: Back to the Roots

Area of Science:

• Physical Chemistry
• Chemical Physics
• Spectroscopy

Background:

• Potential-energy surfaces (PES) are fundamental to understanding chemical reactions and spectroscopy.
• Common terminology like "adiabatic" and "Born-Oppenheimer" approximations are often used inconsistently.
• The Franck-Condon principle (FCP) also suffers from varied interpretations, leading to confusion in scientific literature.

Purpose of the Study:

• To clarify the precise meaning and application of terms related to potential-energy surfaces.
• To address the historical and conceptual inconsistencies in the use of Born-Oppenheimer and Franck-Condon terminology.
• To encourage a more rigorous and accurate understanding of these foundational concepts in physical chemistry.

Main Methods:

• Revisiting original seminal publications on potential-energy surfaces.
• Analyzing the historical development and original definitions of the Born-Oppenheimer approximation.
• Examining the foundational papers and definitions related to the Franck-Condon principle.

Main Results:

• Identified widespread misuse and ambiguous interpretations of key terms like "Born-Oppenheimer approximation" and "Franck-Condon principle".
• Highlighted discrepancies between original theoretical formulations and current applications of these concepts.
• Revealed the need for precise definitions to avoid confusion in spectroscopy, photochemistry, and chemical kinetics.

Conclusions:

• Accurate and consistent terminology is crucial for advancing the fields of spectroscopy, photochemistry, and chemical kinetics.
• A return to the original definitions of the Born-Oppenheimer approximation and Franck-Condon principle is advocated.
• Clearer conceptual understanding will foster more accurate theoretical and experimental work.