研究目的
Characterizing the charge resonance interaction in aromatic dimer radical ions using vibrational infrared spectroscopy to probe the charge distribution by measuring the frequency of the isolated NH stretch mode (νNH).
研究成果
The study demonstrates that the νNH frequency of the free Py unit is a sensitive indicator of its partial charge, allowing the quantitative experimental determination of the charge asymmetry in modified Py2 + clusters. This general concept can be applied to other arene cluster cations (and also anions) exhibiting the CR interaction.
研究不足
The study focuses on pyrrole dimer cations and their modifications, which may limit the generalizability of the findings to other aromatic systems. The IRPD technique requires clusters with certain internal energy to undergo dissociation, which may affect the observed frequencies.
1：Experimental Design and Method Selection:
The study combines IR photodissociation (IRPD) spectroscopy of mass-selected cluster ions generated in a cold molecular beam with dispersion-corrected density functional theory calculations (B3LYP-D3/aug-cc-pVTZ) to probe the geometric, vibrational, and electronic properties of pyrrole clusters.
2：Sample Selection and Data Sources:
Cluster ions of interest were size-selected by the first quadrupole and irradiated in an adjacent octupole with a tuneable IR laser pulse.
3：List of Experimental Equipment and Materials:
A tandem quadrupole mass spectrometer coupled to an electron ionization source was used. Cluster ions were generated in a pulsed supersonic plasma expansion of Py and NMPy seeded in N2, Ar, or He carrier gas.
4：Experimental Procedures and Operational Workflow:
Resonant vibrational excitation induced dissociation, and the resulting fragment ions filtered by the second quadrupole were monitored as a function of νIR to derive the IRPD spectra of the parent ions.
5：Data Analysis Methods:
Quantum chemical calculations were carried out at the dispersion-corrected B3LYP-D3/aug-cc-pVTZ level. The atomic charge distribution was evaluated using the NBO analysis.
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