On the basis of CCSD(T) calculations, an accurate equilibrium geometry has been established for linear NC5NC: R-1e(NC) = 1.1615 Angstrom, R-2e = 1.3705 Angstrom, R-3e = 1.2134 Angstrom, R-4e = 1.3607 Angstrom, R-5e = 1.2102 Angstrom, R-6e = 1.3047 Angstrom and R-7e(NC) = 1.1831 Angstrom, with uncertainties on the order of 0.0005 Angstrom. The ground-state rotational constant is predicted to be 580.2 +/- 0.2 MHz and the equilibrium dipole moment is obtained to be mu(e) = 1.38 D. In agreement with matrix isolation IR spectroscopy, only three intense vibrational transitions are calculated for the most abundant isotopomer between 2000 and 2300 cm(-1) Inclusion of anharmonicity effects is mandatory to obtain this result; an unusual anharmonicity effect between the fundamentals nu(1) and nu(2) is predicted. Isotopic substitution significantly changes the intensities of the two stretching vibrational bands with highest wavenumber.