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.

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Ocean Optics HR4000 spectrometer model with user-configured options installed: TCD1304AP (DET4-VIS) detector with VIS window with detector collection lens (L4); 5-μm slit width (SLIT-5); 2400 line holographic VIS grating (H12) with bandwidth 365-455 nm. oceanview software is used to manually configure the acquisition parameters. Including the fiber (P600-2-UV-VIS) with collimating lens (74-UV) the price for HR4000 was about 5814.00 in 2013.

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