[¹³C ii] spectra calibrated in main beam brightness temperature and plotted on a common V_lsr scale of [¹³C ii]. On the left is the long integration HIFI spectrum toward HD 37903. The F = 2−1 is plotted in black and F = 1−0 in red overlaid with Gaussian fits in green. To the right is an average of all GREAT [C ii] spectra brighter than 35 K in the SE quadrant of our map of NGC  2023. The F = 2−1 line is clearly visible at V_lsr = 10.1 km s^-1, see text. The temperature scale is in T_mb (K).