研究目的
To investigate the effect of functional group substitution (specifically, replacing hydroxyl with thiol group) on the yield and formation time scales of H3+ ions produced via H2 roaming mechanisms during strong-field photodissociation of organic molecules, using ethanethiol and ethanol as comparative cases.
研究成果
The substitution of a thiol group for a hydroxyl group in organic molecules leads to a significant reduction in H3+ yield and an increase in formation time during strong-field photodissociation, due to less favorable electronic and structural changes upon double ionization. These findings provide insights into roaming mechanisms in ionic species and have implications for understanding chemical reactions in interstellar media.
研究不足
The study is limited to gas-phase reactions under strong laser fields, which may not fully represent conditions in interstellar or atmospheric environments. The intensity calibration has an uncertainty factor of 2, and measurements are subject to noise in differential yield analysis. The computational methods rely on specific levels of theory (e.g., CCSD/aug-cc-pVDZ) which may not capture all electronic effects accurately.
1：Experimental Design and Method Selection:
The study employs strong-field photodissociation using a 40-fs 800-nm laser pulse to induce dissociative ionization. Time-of-flight mass spectrometry is used for ion analysis, with femtosecond pump-probe transients for time-resolved measurements. Ab initio quantum mechanical calculations (CCSD, CR-CC(2,3), EOM-CCSD) support experimental findings.
2：Sample Selection and Data Sources:
High-purity liquid samples of ethanol (CH3CH2OH), ethanethiol (CH3CH2SH), and their deuterated isotopologues (CH3CH2OD, CH3CH2SD) are used. Samples are dehydrated and outgassed to minimize contaminants. Data is acquired from mass spectra and transient measurements.
3：List of Experimental Equipment and Materials:
A time-of-flight mass spectrometer, a Mach-Zehnder interferometer for pump-probe setup, a laser system producing 40-fs 800-nm pulses, high-purity chemical samples, molecular sieve desiccants, and vacuum equipment.
4：Experimental Procedures and Operational Workflow:
Laser intensity is calibrated using Ar2+/Ar+ and N22+/N2+ yield ratios. Samples are introduced into the interaction region at controlled pressure (1.0 ± 0.5 × 10^{-6} Torr). Mass spectra are recorded for intensity-dependent yields, and pump-probe delays are varied for transient measurements to extract formation time scales.
5：0 ± 5 × 10^{-6} Torr). Mass spectra are recorded for intensity-dependent yields, and pump-probe delays are varied for transient measurements to extract formation time scales.
Data Analysis Methods:
5. Data Analysis Methods: Differential ion yield analysis is performed to account for Gaussian intensity distribution. Exponential fits are applied to transient data to determine formation time constants. Statistical error propagation is used for uncertainty estimates.
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