Ultrafast Transient Cyclization of Doubly Charged Acetonitrile

Area of Science:

• Physical Chemistry
• Chemical Physics
• Computational Chemistry

Background:

• Understanding molecular dynamics is crucial for predicting chemical reactions.
• Doubly ionized molecules exhibit unique and complex behaviors.
• Acetonitrile is a common organic solvent with various applications.

Purpose of the Study:

• To investigate the isomerization dynamics of doubly ionized acetonitrile ([H₃C─C≡N]²⁺).
• To explore the structural transformations and timescales involved in the dication's rearrangement.
• To compare theoretical predictions with experimental observations.

Main Methods:

• Joint theoretical and experimental investigation.
• Molecular dynamics simulations to model the dication's behavior.
• Femtosecond (fs) pump-probe experiments utilizing Coulomb explosion imaging.

Main Results:

• The doubly ionized acetonitrile dication maintains a linear geometry for hundreds of femtoseconds.
• A rapid cyclization process (<30 fs) forms a triangular geometry.
• The dication adopts an irreversible linear isonitrile (C─N─C) configuration.

Conclusions:

• The isomerization dynamics of doubly ionized acetonitrile are characterized by fast cyclization and irreversible structural changes.
• Theoretical simulations align with experimental findings from fs pump-probe spectroscopy.
• The study provides insights into the complex behavior of small polyatomic dications.