研究目的
Investigating the dynamics of chlorine atom formation in the photodissociation of halogenated pyrimidines at 235 nm, focusing on translational energy distribution, anisotropy parameter, spin-orbit branching ratio, and the role of triplet states.
研究成果
The photodissociation of halogenated pyrimidines at 235 nm primarily occurs through ground state dissociation with minor contributions from excited triplet states, as indicated by translational energy distributions and anisotropy parameters. The average translational energies and spin-orbit branching ratios were quantified, and computational studies supported the role of triplet states. This provides insights into the dissociation mechanisms of heterocyclic compounds.
研究不足
The study is limited to specific halogenated pyrimidines and 235 nm excitation; generalizations to other wavelengths or compounds may not hold. Experimental uncertainties in measurements (e.g., ±1.2 kcal/mol for translational energy) and computational approximations (e.g., EOM-CCSD method) could affect accuracy. The assumption of planar dissociation and preserved symmetry in computations may not fully capture real molecular dynamics.
1：Experimental Design and Method Selection:
The study used Resonance Enhanced Multiphoton Ionisation Time-of-Flight Mass Spectrometry (REMPI-TOF-MS) in a molecular beam to detect Cl atoms. A forward convolution technique was employed to analyze time-of-flight profiles and determine translational energy distributions and anisotropy parameters. Computational methods included EOM-CCSD for potential energy curves.
2：Sample Selection and Data Sources:
Samples were 2,4,6-trichloropyrimidine (97% purity, Sigma-Aldrich) and 5-chloro-2,4,6-trifluoropyrimidine (99% purity, Sigma-Aldrich), used without further purification. Data were collected from laser-induced photodissociation and ionization experiments.
3：List of Experimental Equipment and Materials:
Equipment included a pulsed molecular beam system, dye laser (rhodamine 101 dye), Nd:YAG laser, KDP crystal for frequency doubling, Wiley-McLaren TOF mass spectrometer, dual microchannel plates (MCP), polarizer, double Fresnel rhomb, photodiodes (Becker and Heckl, PDM-400), and a UV spectrophotometer for absorption spectra.
4：Experimental Procedures and Operational Workflow:
A molecular beam of the compound in helium was photolyzed at 235 nm using a laser beam that also served as the probe for ionization via 2+1 REMPI scheme. TOF profiles were recorded at different laser polarizations, with data averaged over multiple laser shots. Power dependence and polarization experiments were conducted, and Doppler profiles were scanned for spin-orbit states.
5：Data Analysis Methods:
Data were analyzed using forward convolution to fit TOF profiles, considering instrumental response functions. Translational energy distributions were derived, and anisotropy parameters were calculated. Computational data from EOM-CCSD simulations were used to interpret results.
独家科研数据包，助您复现前沿成果，加速创新突破
获取完整内容-
Nd:YAG laser
Pumping the dye laser to generate 532 nm light for frequency doubling and mixing to produce 235 nm laser light.
-
Dye laser
Generating laser light using rhodamine 101 dye, pumped by Nd:YAG laser, for photodissociation and ionization.
-
KDP crystal
Frequency doubling the dye laser output to achieve UV wavelengths.
-
Wiley-McLaren TOF mass spectrometer
Detecting ions generated from REMPI, with extraction and acceleration regions for time-of-flight measurements.
-
Microchannel plates
MCP
Detecting ions in the TOF mass spectrometer.
-
Polarizer
Ensuring high polarization of the laser beam for anisotropy experiments.
-
Double Fresnel rhomb
Rotating the polarization of the laser beam.
-
Photodiodes
PDM-400
Becker and Heckl
Measuring laser intensity in absorption cross-section experiments.
-
UV spectrophotometer
Recording absorption spectra of the compounds.
-
Capacitance manometer
Measuring sample pressure in absorption cross-section cell.
-
Boxcar integrator
Integrating mass-gated chlorine atom REMPI signals for power dependence studies.
-
登录查看剩余9件设备及参数对照表
查看全部
