Collisional processes in the O2 B 3Σu− state

Collisional processes, which influence quantitative laser-induced fluorescence (LIF) measurements involving the B 3Σu− state of molecular oxygen, were investigated. Since the B state is strongly predissociating, these processes are though to be important only at higher pressure. However, we found that in LIF experiments in methane/air flames in the pressure range between atmospheric pressure and 40 bar collisional quenching and rotational energy transfer (RET) are important even at moderate pressures. Total quenching cross sections of 30(± 10) Å2 for ν′ = 2 and 100(± 30) Å2 for ν = 0 and total RET cross sections of 40(± 16) Å2 were found. An upper limit of 0.7 Å2 for the cross section for vibrational energy transfer (VET) out of ν′ = 2 could be determined.