Related Experiment Video
Updated: Aug 12, 2025
06:53
Photoelectron Imaging of Anions Illustrated by 310 Nm Detachment of F−
Published on: July 27, 2018
8.8K
Electronic effects in the dissociative ionisation of pyrene clusters
Gustavo A Garcia1, Léo Dontot2,3, Mathias Rapacioli3
1Synchrotron SOLEIL, L'Orme des Merisiers, Départamentale 128, 91190 Saint Aubin, France. gustavo.garcia@synchrotron-soleil.fr.
Physical Chemistry Chemical Physics : PCCP
|February 1, 2023
Summary
We studied how pyrene clusters break apart after ionization. Results show non-statistical dissociation, suggesting excited states influence fragmentation, impacting astrophysical cluster stability.
Area of Science:
- Physical Chemistry
- Astrochemistry
- Quantum Mechanics
Background:
- Polycyclic Aromatic Hydrocarbons (PAHs) are abundant in space.
- Understanding PAH cluster stability is crucial for astrochemistry.
- Dissociative ionization is a key process affecting molecular clusters.
Purpose of the Study:
- Investigate the dissociative ionization of pyrene clusters.
- Determine if dissociation follows statistical or non-statistical pathways.
- Assess the role of electronic excited states in fragmentation.
Main Methods:
- Experimental measurement of appearance energies for pyrene clusters (up to hexamer) using photon energies from 7.2-12.0 eV.
- Theoretical electronic structure calculations to model dissociation pathways.
- Analysis of experimental data in conjunction with theoretical insights.
Main Results:
- Observed deviation from statistical dissociation in pyrene clusters.
- Identified the significant influence of electronic excited states on fragmentation patterns.
- Experimental appearance energies did not align with purely statistical models.
Conclusions:
- Dissociative ionization of pyrene clusters is non-statistical.
- Electronic excited states play a critical role, even in larger systems.
- Non-statistical effects impact the stability assessment of PAH clusters in astrophysical environments.
Related Concept Videos
01:21Chemical Ionization (CI) Mass Spectrometry
822
The molecular ion peak of a molecule in the mass spectrum provides vital information for molecular identification. However, conventional electron impact ionization can lead to the rapid dissociation of some molecular ions before they reach the detector. A milder ionization method is required to increase the lifetime of such ionized analyte molecules. Chemical ionization (CI) is a gas-phase protonation reaction useful for mass-analyzing analyte molecules that are easily protonated to yield the...
822
01:27π Electron Effects on Chemical Shift: Overview
1.1K
An applied magnetic field causes loosely bound π-electrons in organic molecules to circulate, producing a local or induced diamagnetic field over a large spatial volume. As the molecules tumble in solution, the field generated by π-electrons in spherical substituents results in a zero net field. However, the net field generated by π-electrons in non-spherical substituents is not zero. The effect of this induced field depends on the orientation of the molecule with respect to B0,...
1.1K
01:14π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds
1.2K
In aromatic compounds, such as benzene, the circulation of (4n + 2) π-electrons sets up a diamagnetic or diatropic ring current around the perimeter of the molecule. This current induces a magnetic field that opposes the external field inside the ring and reinforces it on the outside. The protons in benzene are deshielded and exhibit high chemical shifts in the range 6.5–8.5 ppm. The shielding effect at the center of the ring is evident in complex aromatic molecules, such as...
1.2K
01:20Mass Spectrometry: Molecular Fragmentation Overview
3.5K
The ionization of a molecule into a molecular ion inside the mass spectrometer causes instability in the molecule's structure due to the loss of an electron. This eventually leads to the fragmentation or breaking of some bonds in the molecule. The fragmentation occurs predominantly at specific bonds to yield relatively stable fragments.
One type of fragmentation pattern is the cleavage of a single bond in the molecular ion. The cleavage leads to a radical and a cation. The cleavage can...
One type of fragmentation pattern is the cleavage of a single bond in the molecular ion. The cleavage leads to a radical and a cation. The cleavage can...
3.5K
01:20¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)
1.1K
When proton-coupled carbon-13 spectra are simplified by a broadband proton decoupling technique, structural information about the coupled protons is lost. Distortionless enhancement by polarization transfer (DEPT) is a technique that provides information on the number of hydrogens attached to each carbon in a molecule. While the DEPT experiment utilizes complex pulse sequences, the pulse delay and flip angle are specifically manipulated. The resulting signals have different phases depending on...
1.1K
01:17Electron Paramagnetic Resonance (EPR) Spectroscopy: Organic Radicals
2.6K
Ideally, an unpaired electron shows a single peak in the EPR spectrum due to the transition between the two spin energy states. However, coupling interactions can occur between the spins of the unpaired electron and any neighboring spin-active nuclei. This hyperfine coupling results in hyperfine splitting, where the EPR signal is split into multiplets. The signals split into 2nI + 1 peaks, where n is the number of equivalent nuclei and I is the nuclear spin. These splitting patterns provide...
2.6K