Kinetic behaviour of electronically excited tin atoms, Sn(51S0, 51D2), and the importance of (J,Ω) coupling in heavy atom–molecule collisions

Abstract

An experimental investigation, principally of the collisional behaviour of electronically excited tin atoms in the (5p²¹S₀) state, together with some additional measurements of the (5p²¹D₂) state, is presented. The optically metastable atoms were generated by pulsed irradiation and monitored photoelectrically in absorption by time-resolved attenuation of atomic resonance radiation using rapid response precision logarithmic circuitry. Quenching rate constants are determined for a wide range of collision partners. The resulting data for the ¹S₀ state are compared with those for Sn (5¹D₂) and also with the analogous data for the (6p^{2 1}S₀) and (6p^{2 1}D₂) states of atomic lead. The collisional behaviour of the ¹S₀ and ¹D₂ states of both tin and lead are discussed in terms of symmetry arguments based on (J,Ω) coupling. This is shown, as expected, to be a more suitable vehicle for considering the chemistry of heavy metal atoms compared with similar arguments used hitherto for light atoms where the weak spin orbit coupling approximation has been employed.