Ultra-Low-Temperature Reactions of Carbon Atoms with Hydrogen Molecules

TL;DR

This study investigates the reactions of carbon atoms with hydrogen molecules at ultra-low temperatures using calorimetry and mass spectrometry, revealing barrierless reactions and stable hydrocarbon cations relevant to interstellar chemistry.

Contribution

It provides new experimental evidence of barrierless reactions and stable hydrocarbon cations formed at near absolute zero temperatures, advancing understanding of interstellar chemistry.

Findings

Detected barrierless reaction between carbon atom and hydrogen molecule.

Observed formation of stable hydrocarbon cations, including CH5+.

Identified high abundance of CH5+ in mass spectra, relevant to interstellar medium.

Abstract

The reactions of carbon atoms with dihydrogen have been investigated in liquid helium droplets at $T$ = 0.37 K. A calorimetric technique was applied to monitor the energy released in the reaction. The barrierless reaction between a single carbon atom and a single dihydrogen molecule was detected. Reactions between dihydrogen clusters and carbon atoms have been studied by high-resolution mass spectrometry. The formation of hydrocarbon cations of the type C$_m$H$_n^+$, with $m$ = 1-4 and $n$ = 1-15 was observed. With enhanced concentration of dihydrogen, the mass spectra demonstrated the main "magic" peak assigned to the CH$_5^+$ cation. A simple formation pathway and the high stability of this cation suggest its high abundance in the interstellar medium.