Ultra-high-resolution observations of interstellar C-2, CH and CN towards zeta Ophiuchi and HD 169454

We have used the Ultra-High-Resolution Facility (UHRF) at the Angle-Australian Telescope (AAT), operating at a resolution of 0.33 km s(-1) (FWKM), to observe lines arising from the five lowest rotational levels of interstellar C-2 towards zeta Ophiuchi and HD 169454. We have also obtained new observations of CH and CN towards the latter star. The very high spectral resolution has enabled us to perform a rotational excitation analysis for both of the closely spaced velocity components (separation 1.1 +/- 0.1 km s(-1)) known to be present towards zeta Oph, and, contrary to earlier results based on an analysis of only two lines, we show that these components have very similar physical conditions. In the case of HD 169454, we confirm the presence of two very closely spaced velocity components (separation 0.7 +/- 0.1 km s(-1)) in both the C-2 and the CN lines. We have determined the turbulent velocities directly from the line profiles. In all cases we find values in the range 0.23-0.45 km s(-1), and there is no convincing evidence for supersonic turbulence in any of the identified velocity components.