The Schumann-Runge O2 Emission, Following Visible Multiphoton Excitation of NO2

The Schumann-Runge emission ( B 3 Σ u −  −  X 3 Σ g − ) of oxygen was observed in the wavelengthrange of 220–300 nm, when NO 2 was irradiated with a focused visible laser (470–580 nm).The excitation spectrum of the emission also showed the Schumann-Runge transition from highly excited vibrational levels (v″ = 22–26) of the X state to the v′ = 1–3 levels of the B state of oxygen. The highly vibrationally excited O 2 ( E v i b≃ 30000 cm −1 ) is once produced through a multiphoton process of NO 2 and then absorbs one more photon. The resulting excited state of O 2 emits fluorescence in the UV region. Even at 40 torr of NO 2 , no rotational-vibrational relaxation in the B state was observed. The mechanism of the multiphoton process is discussed.