Visualizing competing intersystem crossing and internal conversion with a complementary measurement.

Area of Science:

• Chemical Physics
• Molecular Dynamics
• Spectroscopy

Background:

• Investigating ultrafast dynamics of electronically excited states is crucial for understanding chemical reactions.
• The second singlet excited state (S2) in molecules like m-xylene plays a key role in photochemical processes.

Purpose of the Study:

• To introduce and validate a novel double-sided velocity map imaging technique for simultaneous time-resolved photoelectron and fragment ion imaging.
• To elucidate the ultrafast dynamics and deactivation pathways of the S2 state in m-xylene.

Main Methods:

• Development of a home-built double-sided velocity map imaging setup.
• Utilizing a pump-probe spectroscopy approach with two-photon absorption.
• Analysis of time-resolved photoelectron and fragment ion images, including kinetic and angular distributions.

Main Results:

• Simultaneous time-resolved photoelectron and fragment ion imaging of m-xylene's S2 state was achieved.
• Dominant parent ions and methyl-loss fragment ions were observed.
• Intersystem crossing (T3←S2) and internal conversion (S1←S2) were identified as competing deactivation channels for the S2 state.

Conclusions:

• The developed method provides enhanced mechanistic understanding, especially for dissociative processes during pump-probe ionization.
• Lifetimes for the S2 state (~50 fs), S1 state (~276 fs), and T3 state (~5.76 ps) were determined.
• This technique offers a powerful complementary approach to stand-alone photoelectron imaging for studying complex molecular dynamics.