Portions of the millimeter-wave rotational spectra of isocyanoacetonitrile (upper scale, dark blue), and malononitrile (lower scale, red). The lines of malononitrile illustrate the effect of symmetry and nuclear spin statistics as their intensities are related as 7-to-5 depending on the K_a + K_c values, whereas the intensities of the lines of isocyanoacetonitrile are not subjected to spin statistics owing to reduced symmetry.