Ultrafast Cation-Dication Dynamics in Ammonia Borane: H-Migration to Roaming H₂ and Reduced H₃⁺ Formation under...

Area of Science:

• Physical Chemistry
• Chemical Physics
• Materials Science

Background:

• Ammonia borane (BH3NH3) is a hydrogen-rich material with potential applications in hydrogen storage.
• Understanding its fragmentation pathways under strong-field ionization is crucial for predicting its behavior and optimizing its use.

Purpose of the Study:

• To investigate the ultrafast fragmentation dynamics of ammonia borane (AB) following single and double ionization using femtosecond time-resolved strong-field techniques.
• To elucidate the molecular origins of neutral and ionic hydrogen-containing products.

Main Methods:

• Femtosecond time-resolved mass spectrometry.
• Ab initio molecular dynamics simulations.
• Electronic-structure calculations.

Main Results:

• Single ionization of AB yields neutral H and H2. Double ionization produces H, H2, H+, H2+, and H3+ within 1 picosecond.
• Hydrogen fragments predominantly originate from hydrogen atoms bonded to the boron center.
• Formation pathways involve hydrogen migration and neutral H2 roaming, with H3+ formation suppressed due to competing H2 dissociation.

Conclusions:

• The study reveals detailed dissociative ionization mechanisms in ammonia borane.
• Findings extend mechanistic principles from other molecules to AB, offering insights into hydrogen release.
• Results have implications for hydrogen storage materials and astrochemistry, particularly concerning H3+ formation.