Penning-like Energy Transfer between Argon and Nitrogen

Nitrogen is known as a gas that has many emission spectra in ultraviolet region named 2nd positive band and they are thought to be suitable for phosphor excitation instead of harmful mercury. However, a molecular gas in a discharge has a tendency to get a high temperature because energy is stored as vibrational and rotational energy. This is a serious problem when the nitrogen discharge is used for light sources. Moreover, nitrogen requires fairy higher voltage to ignite and maintain a discharge compared with mercury-argon mixture. Because argon metastable levels (11.5 eV and 11.7 eV) lie near nitrogen C³II_u level (11.05 eV), which is upper state of 2nd positive band, energy transfer from argon metastable to nitrogen C ³II_u state is expected in the nitrogen-argon discharge. By limiting the amount of nitrogen to small portion, which is like a relationship between mercury and argon as a Penning gas, the discharge becomes stable and the temperature decrease, whereas the positive column of pure nitrogen or pure argon discharge tend to shrink and the pure nitrogen discharge have a high temperature. This result is attributed to the efficient energy flow to the C³II_u level through the energy transfer mentioned above. However, there is another problem that the amount of nitrogen molecule decreases during discharge, possibly by adsorption of nitrogen to the wall of discharge tube or the electrodes, which is confirmed from decrease in intensity of nitrogen molecule emission. The mechanisms of decrease in nitrogen molecule are under investigation