Modeling Photodissociation: Quantum Dynamics Simulations of Methanol

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Photochemistry

Background:

• Understanding molecular photodissociation dynamics is crucial for various chemical processes.
• Methanol photodissociation serves as a fundamental model system for studying fundamental chemical reactions.

Purpose of the Study:

• To computationally investigate the gas-phase photodissociation dynamics of methanol.
• To elucidate the dependence of dissociation pathways on excitation energy and electronic state.
• To provide a general workflow for modeling photochemical reactions.

Main Methods:

• Multiconfigurational active space based method (RASSCF) for potential energy surfaces (PESs).
• Direct quantum dynamics simulations using the variational multi-configurational Gaussian (DD-vMCG) method.
• Analysis of diabatic surfaces and electronic state couplings.

Main Results:

• Excitation to the lowest lying excited state leads to dominant hydroxyl hydrogen loss (O-H bond breaking).
• Higher energy excitations predominantly result in carbon-oxygen bond (C-O) breaking.
• PES analysis confirms the dissociative nature along O-H stretch for low-energy excitation.

Conclusions:

• Methanol photodissociation pathways are strongly dependent on excitation energy.
• The study provides a mechanistic explanation for observed branching ratios.
• The presented computational workflow is applicable to modeling other photochemical reactions.