Internal conversion rate constant calculations considering Duschinsky, anharmonic and Herzberg-Teller effects

Area of Science:

• Computational Chemistry
• Photochemistry
• Spectroscopy

Background:

• Internal conversion (kIC) is a key nonradiative decay process in excited molecules.
• Accurate calculation of kIC requires considering complex vibronic coupling effects.

Purpose of the Study:

• To develop and implement a novel method for calculating kIC.
• To simultaneously account for Duschinsky, anharmonic, and Herzberg-Teller effects.

Main Methods:

• Developed a new computational method for kIC calculations.
• Applied the method to molecules with varying Duschinsky rotation (4B, H2P, PM567, PnF).

Main Results:

• Anharmonic contributions to kIC are larger than Herzberg-Teller, which are larger than Duschinsky effects (ANH > HT > Du).
• Duschinsky effect is significant in harmonic approximation but smaller in anharmonic approximation.
• An approximation focusing on X-H bonds proves accurate for kIC calculations.

Conclusions:

• The developed method provides accurate kIC calculations.
• Anharmonic effects play a dominant role in internal conversion.
• Simplified approximations considering X-H bonds are effective.