Profiles of the lambda 6196 and lambda 6379 diffuse interstellar bands

We have looked for rotational structure in the sharp lambda 6196 and lambda 6379 diffuse interstellar bands (DIBs) at a resolution similar to 120,000 in seven stars where the interstellar lambda 7699 K I line is unresolved. T he lambda 6196 DIB is bell-shaped with a flat core and differs slightly in width from star to star. It is accompanied by a weak DIB at lambda 6194.7, with which it does not maintain a constant depth ratio. The lambda 6379 DIB is asymmetric with a sharp double core, but the profile hardly varies betw een the stars apart from being undetectable for HD 37061. Weak features con nect it to the weaker lambda 6376 DIB, with which it varies in unison. Simp le rotational models do not fit the observed profiles of lambda 6196 and la mbda 6376 at all well because of more prominent branch structure in the mod els. We achieve an acceptable fit by arbitrarily convolving the modeled pro files with Gaussians (0.2 to 0.3 cm(-1)). The Gaussians correspond to an un expected or anomalous broadening process that cannot be explained by the in terstellar velocity distribution or the instrumental point-spread function. The fits give upper limits to the ratio of the rotational temperature to t he moment of inertia of the molecular carriers. If the former lies in the r ange 10-100 K, then the molecules must be large, with moments of inertia co mparable with that of the fullerene C-60. We present evidence that the anom alous broadening of the rotational profiles is intramolecular in origin, bu t it is not easily explained by broadening processes previously invoked in connection with the DIBs. We suggest that some other process such as a zero -point vibrational isotope shift may be involved that could be characterist ic of many of the narrow bands.