研究目的
Investigating the ultrafast nonadiabatic cascade and subsequent photofragmentation of extreme ultraviolet excited caffeine molecule to understand fundamental natural phenomena such as molecule formation in interstellar media.
研究成果
The study demonstrates that the XUV-excited caffeine molecule undergoes a relaxation cascade through more than 100 monocationic shake-up states with a time constant of about 40 fs. This dynamics drastically changes the photofragmentation process after the IR probe radiation, showing that complex highly correlated electronic structure and nonadiabatic couplings are key ingredients to understand ultrafast reaction dynamics in highly excited molecules.
研究不足
The study is limited by the complexity of the highly excited molecular states and the need for advanced quantum chemistry calculations to interpret the observed dynamics.
1：Experimental Design and Method Selection:
The experiment used ultrashort XUV light pulses for XUV-pump–IR-probe experiments in caffeine. The methodology involved time-dependent mass spectrometry to resolve the dynamics induced by the XUV excitation on the femtosecond timescale.
2：Sample Selection and Data Sources:
Neutral caffeine was obtained in the gas phase by sublimation of a solid sample. The central photon energy for HHG in xenon was around 25 eV.
3：List of Experimental Equipment and Materials:
The setup included an amplified laser system delivering 25 fs pulses, a hollow fiber for spectral broadening, a gas cell for high harmonics generation, metallic foils for filtering XUV light, and a velocity map imaging spectrometer.
4：Experimental Procedures and Operational Workflow:
The XUV and IR beams were focused in the interaction chamber where they crossed the molecular beam. The cross-correlation between the XUV and IR beam was estimated to be 25 fs.
5：Data Analysis Methods:
The variation of the ion yield was measured as a function of the XUV-IR pump-probe delay. The data was fitted to extract decay durations.
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