  We describe an inexpensive instructional experiment that demonstrates the
rotational energy levels of diatomic nitrogen, using the emission band spectrum
of molecular nitrogen ionized by various processes in a commercial AC capillary
discharge tube. The simple setup and analytical procedure is introduced as part
of a sequence of educational experiments employed by a course of advanced
atomic and molecular spectroscopy, where the study of rotational spectra is
combined with the analysis of vibrational characteristics for a multifaceted
picture of the quantum states of diatomic molecules.
