Do the interstellar molecules CCCO and CCCS rearrange when energised?

Area of Science:

• Physical Chemistry
• Chemical Physics
• Mass Spectrometry

Background:

• Neutral molecules CCCO, CC(13)CO, CCCS, and CC(13)CS were synthesized.
• The stability of these neutrals was assessed using the neutralisation-ionisation ((-)NR(+)) experiment.

Purpose of the Study:

• To investigate the stability and reactivity of neutral carbon-chain molecules.
• To study cationic rearrangements in isotopically labeled CCCO and CCCS.
• To elucidate the mechanisms of these rearrangements using theoretical calculations.

Main Methods:

• Preparation of neutral molecules via one-electron vertical oxidation of precursor anion radicals.
• Utilisation of a reverse sector mass spectrometer for the neutralisation-ionisation experiment.
• Theoretical calculations at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory.

Main Results:

• Neutrals CCCO, CC(13)CO, CCCS, and CC(13)CS are stable for the microsecond duration of the (-)NR(+) experiment.
• No label rearrangement was observed in energised CC(13)CO and CC(13)CS cations.
• Minor rearrangement of (CC(13)CO)(+*) to (OCC(13)C)(+*) and significant rearrangement of (CC(13)CS)(+*) to (SCC(13)C)(+*) were observed.
• Theoretical calculations confirmed stepwise cationic rearrangements via rhombic structures, involving O and S migration from C-3 to C-1.

Conclusions:

• The prepared neutral molecules are sufficiently stable for experimental investigation.
• Cationic rearrangements in CCCO+ and CCCS+ involve atom migration and proceed through specific intermediate structures.
• Significant energy is required for these cationic rearrangements to occur.