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

Abstract

The Schumann-Runge emission (B3Σu− − X3Σg−) of oxygen was observed in the wavelength range of 220–300 nm, when NO2 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 O2 (Evib ≃ 30000 cm−1) is once produced through a multiphoton process of NO2 and then absorbs one more photon. The resulting excited state of O2 emits fluorescence in the UV region. Even at 40 torr of NO2, no rotational-vibrational relaxation in the B state was observed. The mechanism of the multiphoton process is discussed.