Microwave Electric Field Dependent Visible Emission Spectra in a Collisional N2 Plasma

The visible line spectra for nitrogen plasma in the collisional regime (20Torr) was investigated for electric field influence. Nitrogen plasma was induced in the capacitive gap of a microwave resonator at 1.46 GHz, and the emission spectra were compared over a range of electric fields. Measurements were made with an astronomical grade spectrometer and the spectra were recorded by a CCD camera and then converted from pixels to wavelengths using imaging software. Only within low wavelength (370nm-450nm range) are transitions in the 2nd positive system (C3Πu – B3Πg) observed. Electronic bandheads from the 1st positive system (B3Πg – A3Σu+) and rotationally degraded wavelength emissions in the medium wavelength (570 nm to 650 nm) range are seen at high and medium electric field, but not at low electric field. This corresponds to the observed color change of the plasma. At low electric field N2 exhibits blue plasma, whereas at high electric field orange plasma is resultant. This can be observed visibly with the naked eye as the electric field strength is varied