Collision-induced fine-structure transitions of Hg(6³P₁ → 6³P₀) with N₂ and CO. 2. Translational energy dependence

Translational energy dependences of relative cross sections for Hg(6³P₁ → 6³P₀) fine-structure changing collisions with N₂ and CO have been measured with a crossed-beam apparatus over the energy range between 800 and 3750 cm^-1. A negative energy dependence is obtained for Hg-CO, but a positive energy dependence is observed for Hg-N₂, with an energy threshold for appearance of Hg(6³P₀) around 900 cm^-1. These results are explained using the characteristics of the intermolecular potentials for Hg-N₂ and Hg-CO. The existence of the energy threshold around 900 cm^-1 for N₂ suggests simultaneous vibrational excitation of N₂. The translational energy dependence has also been measured under beam-gas conditions over the energy range between 450 and 3350 cm^-1. From a comparison with Hg(6³P₁ → 6³P₀) intramultiplet deactivation cross sections for Hg-N₂ and Hg-CO obtained in gas cell experiments, absolute values of the cross sections for this intramultiplet transition are estimated as a function of the average translational energy under the beamgas conditions. There is no clear threshold for Hg-N₂ in the beam-gas experiment and it is suggested that a higher rotational temperature of N₂ induces a shift of the energy threshold effectively lower.