  We present high spectral-resolution observations of comets 122P/de Vico and
153P/Ikeya-Zhang obtained with the Tull Coud\'{e} spectrograph on the 2.7m
Harlan J. Smith telescope of McDonald Observatory. We used these data to study
the distribution of the lines of the $\mathrm{d} ^3\Pi_g - \mathrm{a} ^3\Pi_u$
C$_2$ (Swan) bands. We show that the data are best represented with two
rotational temperatures, with the lowest energy lines being at a relatively
cool temperature and the higher energy lines being at a higher temperature. We
discuss the implications of this two temperature distribution and suggest
future work.
