One-dimensional N₂ gas inside single-walled carbon nanotubes

The unexpected presence of a linear arrangement of co-axially oriented N₂ molecules inside aligned single-walled carbon nanotubes is revealed by high resolution near-edge X-ray absorption spectroscopy. The encapsulated N₂ molecules exhibit free stretching vibrations with a long electronic lifetime of the X-ray-excited anti-bonding π ^* states. Molecular dynamics simulations confirm that narrow-diameter nanotubes (d < 1 nm) are crucial for stabilizing the linear arrangement of aligned N₂ molecules.