研究目的
Investigating how the position of the methyl group influences the ultrafast deactivation processes in aromatic xylyl radicals after excitation into the D3 state.
研究成果
The meta-xylyl isomer deactivates fastest due to access to a conical intersection via ring deformation modes, not methyl rotation. Ultrafast hydrogen loss occurs via absorption of two 4 eV photons, and isomerization from meta to ortho/para is observed at high energies.
研究不足
Low number densities of radicals make signal detection challenging; reliance on intermediate resonances for sensitivity; theoretical predictions limited by state mixing and spin contamination in computations; signal-to-noise levels in some experiments (e.g., (4+4) eV) were too low for detailed analysis.
1：Experimental Design and Method Selection:
Femtosecond time-resolved pump-probe spectroscopy using resonance-enhanced multiphoton ionization (REMPI) to study deactivation dynamics.
2：Sample Selection and Data Sources:
Xylyl radicals (ortho-, meta-, para-isomers) prepared by flash vacuum pyrolysis of xylyl bromide precursors.
3：List of Experimental Equipment and Materials:
Femtosecond laser system (Clark-MXR CPA-1000), optical parametric amplifier, double velocity map imaging spectrometer, SiC tubular reactor, solenoid valve, helium gas, xylyl bromide (Sigma Aldrich).
4：Experimental Procedures and Operational Workflow:
Radicals excited with 310 nm (4 eV) pump pulse, ionized with 790 nm (1.6 eV) or 310 nm (4 eV) probe pulse at variable delays; ions and electrons analyzed using time-of-flight mass spectrometry and velocity map imaging.
5：6 eV) or 310 nm (4 eV) probe pulse at variable delays; ions and electrons analyzed using time-of-flight mass spectrometry and velocity map imaging. Data Analysis Methods:
5. Data Analysis Methods: Fitting of temporal decay curves with exponential functions, analysis of photoelectron spectra using Lin-BASEX algorithm, statistical fitting with 95% confidence intervals.
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