What is a practical and economic way of producing ultra violet light around ionizing frequencies? A tunable light source is preferable in order to adjust the ionization level.
Molecular oxygen ionization energy is according to Journal of Chemical Education, Vol. 80 No. 12 December 2003 p. 1381 1.576*10^-19 Joule per molecule (corresponding to 1260 nanometer wavelength).
This seems like infrared. Does this fit with real observations?