Hydrogen Controls the Heavy Atom Roaming in Transient Negative Ion

Area of Science:

• Physical Chemistry
• Chemical Physics
• Molecular Dynamics

Background:

• Roaming reactions in anions are complex, involving unusual atom mobility.
• The influence of hydrogen's position on reaction dynamics in bromo-triazole anions is not well understood.
• Noncovalent Br- anion complexes around aromatic rings are increasingly recognized in biologically relevant molecules.

Purpose of the Study:

• To investigate the effect of hydrogen position on the dissociation dynamics of 3-bromo-1H-1,2,4-triazole and 3-bromo-4H-1,2,4-triazole anions.
• To elucidate the roles of bromine and hydrogen during electron-induced reactions.
• To understand the formation and influence of Br- noncovalent complexes.

Main Methods:

• Low-energy electron scattering experiments to measure energy-dependent ion yields.
• Quantum chemical calculations to explore reaction pathways and energetics.
• Analysis of dissociation dynamics, including neutral fragment release.

Main Results:

• Significant differences in ion yields were observed between 3-bromo-1H-1,2,4-triazole and 3-bromo-4H-1,2,4-triazole.
• Br atom migration is energetically favored over H atom migration when H is adjacent to Br.
• The formation of a noncovalent Br- complex around the triazole ring facilitates Br migration.
• Hydrogen position influences the lowest resonant state, impacting Br- roaming and hydrogen bromide release.

Conclusions:

• The position of hydrogen on the triazole ring critically controls the dissociation dynamics of bromo-triazole anions.
• Bromine's role as a mobile atom and hydrogen's role as a dissociation moderator are highlighted.
• Understanding these dynamics provides insights into electron-molecule interactions and fragmentation pathways.