Resonance Raman study of polyynes encapsulated in single-wall carbon nanotubes

This work presents a resonance Raman study of polyyne molecules (linear carbon chains) encapsulated inside single-wall carbon nanotubes using many different laser lines. A strong enhancement of the polyyne Raman features is observed around $2.1\mathrm{eV}$, and this result is ascribed to dark electronic transitions of the linear carbon chains that can be observed when they are trapped inside a carbon nanotube. The huge observed energy splitting between bright and dark excited states is ascribed to strong Coulomb effects in this strictly one-dimensional system.

Figure 1

Raman spectra with $2.18\mathrm{eV}$ excitation energy for the different samples: ${\mathrm{C}}_{10}{\mathrm{H}}_2@\mathrm{SWCNT}$ (dotted and top spectra), ${\mathrm{C}}_{12}{\mathrm{H}}_2@\mathrm{SWCNT}$ (dashed and middle spectra), and pristine SWCNT (solid and bottom spectra). The inset shows a larger view of the $P$ bands for the two polyyne samples. The asterisks indicate the most prominent Raman features of SWCNTs

Figure 2

Raman intensity of the $P$ bands for ${\mathrm{C}}_{10}{\mathrm{H}}_2$ (closed triangles) and for the ${\mathrm{C}}_{12}{\mathrm{H}}_2$ (open circles) as a function of laser excitation energy.