Predicted (in red) and observed (in blue) rotational spectrum of ¹³C methylamine between 882 and 908 GHz dominated by ^cQ-type series of transitions with K_a = 6 ← 5. A slight inconsistency between predicted and observed spectrum, which may be visible for some strong lines, is due to source power and detector sensitivity variations. Weak unassigned lines are due to higher excited vibrational states.