Thermal Stability of C4+4nH8 Polycubanes

TL;DR

This study investigates the thermal stability of polycubanes C4+4nH8 with n=2-5, revealing how their decomposition energies decrease with size and questioning the existence of large square-cross-section nanotubes.

Contribution

It provides direct molecular dynamics calculations of lifetimes and activation energies for polycubanes, highlighting size-dependent stability and challenging recent nanotube hypotheses.

Findings

Activation energy decreases with increasing n.

Bicubane and tricubane are stable at liquid nitrogen temperature.

Large polycubanes likely decompose rapidly, questioning their experimental realization.

Abstract

The temperature dependences of the lifetimes of polycubanes C4+4nH8 with n = 2 - 5 up to their decomposition have been directly calculated using the molecular dynamics method. It has been shown that the activation energy of decomposition of these metastable clusters, in which the C-C bonds form an angle of 90^0 that is not characteristic of carbon systems, rapidly decreases with an increase in n due to the lowering of the energy barrier that prevents the decomposition of the clusters. This has cast some doubt on the recently made suggestion that there exist nanotubes (n >> 1) with a square cross section. Nonetheless, the stability of bicubane (n = 2) and tricubane (n = 3) has proved to be sufficient for their existence at the liquid-nitrogen temperature.