A Strategy for Modeling Nonstatistical Reactivity Effects: Combining Chemical Activation Estimates with a Vibrational...

Area of Science:

• Chemical Kinetics
• Computational Chemistry
• Physical Chemistry

Background:

• Statistical approaches like transition state theory explain many reaction kinetics.
• Nonstatistical phenomena arise when vibrational relaxation and reaction dynamics occur on similar timescales.
• Current computational methods like ab initio molecular dynamics and quantum dynamics have limitations in system size and resource intensity.

Purpose of the Study:

• To develop a computationally tractable model for exploring nonstatistical chemical reaction dynamics.
• To provide insights into enhancing or mitigating bottlenecks in vibrational relaxation.
• To offer a middle-ground approach between statistical theories and resource-intensive quantum dynamics.

Main Methods:

• Utilizing a Fermi's golden rule-based model for vibrational relaxation.
• Employing anharmonic coupling constants to describe vibrational energy transfer.
• Calculating trajectories using (quasi)classical ab initio molecular dynamics (as a comparison point).
• Developing a model applicable to medium-sized organic molecules and biological fragments.

Main Results:

• The proposed model successfully extracts qualitative information about nonstatistical phenomena.
• It offers insights into controlling reaction bottlenecks by understanding vibrational relaxation.
• The model is compatible with readily available electronic structure methods.

Conclusions:

• The Fermi's golden rule-based model serves as a promising middle ground for studying complex nonstatistical chemical behaviors.
• It can be used as a screening tool for mode-selective chemistry.
• Challenges remain in quantifying excess energy distribution among vibrational modes.