Structural dynamics effects on the electronic predissociation of alkyl iodides
Marta L Murillo-Sánchez1, Alexandre Zanchet2,3, Sonia Marggi Poullain1,4
1Departamento de Química Física (Unidad Asociada I+D+i al CSIC), Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040, Madrid, Spain.
Scientific Reports
|April 23, 2020
Summary
This study reveals how chemical structure impacts molecular dissociation. Alkyl iodide predissociation lifetimes shorten with increasing size, linked to potential energy curve shifts and non-adiabatic coupling.
Area of Science:
- Chemical Physics
- Molecular Dynamics
- Spectroscopy
Background:
- Understanding the relationship between chemical structure and molecular dissociation is crucial in chemical physics.
- Predissociation dynamics govern the ultrafast decay of excited molecules, influencing chemical reactions and energy transfer.
- Alkyl iodides serve as model systems for studying fundamental photophysical processes due to their accessible electronic states.
Purpose of the Study:
- To investigate the correlation between the chemical structure of linear and branched alkyl iodides and their predissociation dynamics.
- To elucidate the influence of molecular complexity on electronic predissociation lifetimes and anisotropy.
- To support experimental findings with theoretical ab initio calculations of potential energy curves.
Main Methods:
- Femtosecond time-resolved velocity map imaging experiments were performed following excitation at 201 nm (B-band).
- Analysis of iodine fragment images yielded electronic predissociation lifetimes and anisotropy evolution.
- Ab initio calculations of potential energy curves as a function of the C-I bond distance provided theoretical support.
Main Results:
- Similar predissociation pathways were observed for all studied alkyl iodides, involving bound Rydberg states crossing repulsive states.
- The major dissociation channel identified is R + I*(2P1/2), where R represents various alkyl radicals.
- Electronic predissociation lifetimes decrease with increasing linear alkyl radical size, correlating with shifts in potential energy curve crossings.
Conclusions:
- Molecular structure significantly influences predissociation lifetimes in alkyl iodides.
- Non-adiabatic coupling between electronic states, influenced by vibrational modes, plays a key role in the dissociation process.
- Experimental observations are consistent with theoretical predictions, providing a comprehensive understanding of alkyl iodide predissociation.
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