HTFFR kinetic studies of the fate of excited BaO formed in the Ba/N2O chemiluminescent reaction

Abstract

Rate coefficients for quenching kQ and intersystem conversion kT of excited BaO formed in the reaction Ba+N2O(1)→BaO+N2 have been measured for several collision partners. Methods are developed and applied here for obtaining quenching rate coefficients in chemiluminescent reactions involving a reservoir state. Experiments were performed between 450 and 1000 K at 1–120 Torr in a modified high-temperature fast-flow reactor (HTFFR). The rate coefficients (or their upper limits) are, in ml molecule−1 s−1 units: kArQ (600–1000 K) ?3×10−13; kHeQ (460 K) <3×10−13; kN2Q (600 K) = (4.8±2.0) ×10−12; kN2OQ (600 K) = (4.2±1.0) ×10−10; 2.5×10−10?kO2Q (600 K) ?7.0×10−10; kArT (600 K) ?1.5×10−11. Incidental data at ?1000 K indicate that k1?5×10−11, and that the Ba/O2 reaction has about the same rate coefficient. In addition to BaO emission, strong Ba atomic emission arising from energy transfer processes was observed for [Ba]≳1×1013 ml−1 at T?1000 K. Measurements of the spectral distributions of the Ba/N2O chemiluminescence as a function of [Ar], [He], and [N2] yield relations among vibrational relaxation rate coefficients: kv, kT, and kQ for specific BaO(A 1Σ) vibrational levels. The set of reactions currently in use to describe the Ba/N2O chemiluminescence is shown to be inadequate to account for the observed changes in BaO(A 1Σ−X 1Σ) spectral distribution with pressure.