Photo-induced structural dynamics of o-nitrophenol by ultrafast electron diffraction

Area of Science:

• Chemical Physics
• Photochemistry
• Molecular Dynamics

Background:

• o-nitrophenol photolysis is a potential atmospheric source of nitrous acid.
• Previous studies focused on photolysis products and electronic dynamics, not ultrafast nuclear motions.
• The intramolecular proton transfer during non-radiative relaxation remains experimentally unresolved.

Purpose of the Study:

• To directly observe the ultrafast nuclear dynamics of o-nitrophenol during photo-relaxation.
• To spatiotemporally resolve the key steps in the non-radiative decay pathway.
• To elucidate the mechanism of proton transfer-mediated relaxation.

Main Methods:

• Ultrafast electron diffraction (UED) was employed for direct observation.
• Ab initio multiple spawning (AIMS) simulations were used for theoretical support.
• Femtosecond timescale and sub-Angstrom resolution were achieved.

Main Results:

• Direct observation of ultrafast nuclear motions mediating photo-relaxation.
• Spatiotemporal resolution of the loss of planarity after proton transfer.
• Identification of access to a conical intersection between excited and ground states.

Conclusions:

• The study provides the first experimental resolution of nuclear dynamics in o-nitrophenol relaxation.
• Insights into the proton transfer and subsequent loss of planarity mechanism were gained.
• This work advances understanding of photochemical processes in atmospheric chemistry.