Unimolecular fragmentation induced by low-energy collision: statistically or dynamically driven?

Area of Science:

• Chemical Dynamics
• Computational Chemistry
• Mass Spectrometry

Background:

• Doubly charged metal-formamide ions ([M(formamide)](2+)) are relevant in mass spectrometry.
• Understanding their collision-induced dissociation (CID) mechanisms is crucial for interpreting experimental data.

Purpose of the Study:

• To characterize the CID mechanisms of [Ca(formamide)](2+) and [Sr(formamide)](2+) ions.
• To explain the formation of all observed products and the differences between Ca and Sr ions in CID spectra.

Main Methods:

• Combined chemical dynamics simulations and RRKM statistical theory.
• Simulations covered timescales from femtoseconds to picoseconds.
• RRKM theory analyzed longer timescales and statistical reactivity via intramolecular vibrational energy redistribution (IVR).

Main Results:

• Chemical dynamics simulations captured short-time, dynamically driven reactivity, including impulsive collision mechanisms.
• Simulations provided energy transfer amounts and internal energy distributions (vibrational and rotational) of unreacted ions.
• RRKM theory estimated rate constants for reactive pathways based on simulated energy distributions.

Conclusions:

• The multiscale approach successfully accounted for all observed CID products for both [Ca(formamide)](2+) and [Sr(formamide)](2+).
• The study elucidated the differences in CID behavior between the calcium and strontium ions.
• This combined simulation and statistical theory method provides a comprehensive understanding of CID dynamics.