  Long linear carbon chains encapsulated inside carbon nanotubes are a very
close realization of carbyne, the truly one-dimensional allotrope of carbon.
Here we study individual pairs of double-walled carbon nanotubes and
encapsulated linear carbon chains by tip-enhanced Raman scattering. We observe
that the radial breathing mode of the inner nanotube correlates with the
frequency of the carbon chain's Raman mode, revealing that the nanotube
chirality determines the vibronic and electronic properties of the encapsulated
carbon chain. We provide the missing link that connects the properties of the
encapsulated long linear carbon chain with the structure of the host nanotube.
