Kinetics of formation and quenching of 5s4P5/2, Br excited atoms using fluorescence spectrometry

Abstract

Vacuum ultraviolet photolysis of Br₂ was shown to form excited Br 5s⁴P_5/2 and ⁴P atoms by independent primary processes. The quenching of atomic fluorescence emitted by the excited Br atoms has been studied in a flow system at 298 K, in which the steady state concentration of ground state Br 4p⁵²P was less than 10¹⁰ atom cm^–3. Although Br 5s⁴P atoms have too short a radiative lifetime to show quenching at pressures up to 3 kN m^–2, quenching cross sections σ_M(10^–20 m²) were determined for the more metastable Br 5s⁴P_5/2 atoms: σ_He < 0.02; σ_Ar < 0.04; σ_H2= 0.27; σ_N2= 1.8; σ_CO= 2.9; σ_SF6= 28; σ_Br2= 146. These quenching cross sections are compared with those for quenching of metastable Br 4p⁵²P_½ atoms.