  Ab-initio calculations within Density Functional Theory combined with
experimental Raman spectra on cluster-beam deposited pure carbon films provide
a consistent picture of sp-carbon chains stabilized by sp^3 or sp^2
terminations, the latter being sensitive to torsional strain. This unexplored
effect promises many exciting applications since it allows one to modify the
conductive states near the Fermi level and to switch on and off the on-chain
pi-electron magnetism.
