Optical studies of metal vapours (1982)
AuthorsNokes, Christopher Johnshow all
The kinetics of the CdNH₃* 430 nm emission band at 550 K have been studied using steady-illumination and conventional phase-shift techniques in addition to a laser fluorescence technique that has enabled the phase shift of the metastable Cd (³p₀) species to be measured. The data from these measurements require the system kinetics to be modelled on a mechanism in which an unstabilized complex CdNH₃, having a lifetime in the range 10⁻⁹ - 10⁻¹³ S with respect to dissociation to NH₃ plus either Cd(³P₁) or Cd(³p₀), is present. The phase-shift measurements give values of 2 x 10⁻⁵ s for the radiative lifetime of CdNH3* and 9.1 x 10⁻¹³ cm³ molecule⁻¹ S⁻¹ for the rate constant of the process CdNH*₃ + NH₃ → CdNH₃⁺ + NH₃ The laser fluorescence measurements yield values of 2.1 x 10⁻¹¹ and 8.7 x 10⁻¹¹ cm ³ molecule-¹ s⁻¹ for the rate constants of the processes Cd (³P₀) + NH₃ → CdNH₃ and Cd (³P₁) + NH₃ → CdNH₃ respectively. The steady-illumination measurements show that at low ammonia pressures production of an unstabilized cadmium excimer Cd₂⁺ competes with production of CdNH₃⁺, providing an additional energy reservoir in this system. The lifetime of Cd₂⁺ is two or three orders of magnitude greater than that of CdNH₃.