A high resolution study of the type C(0–0) band of s-tetrazine, C2H2N4, at 5515 Å has revealed regular fine structure in the central qQ branches. The nature of this fine structure is explained using a formula appropriate to high J, low Ka asymmetric top levels and it is shown to be dependent on the change in the rotational constant C between the two states involved. It is suggested that such rotational structure should occur quite frequently in type C bands of larger molecules.