Investigation of the collisional behaviour of electronically excited germanium atoms, Ge[(4p)2(1D2)], by time-resolved atomic resonance absorption spectroscopy in the ultraviolet

Abstract

We present a kinetic investigation of the collisional behaviour of the optically metastable, electronically excited germanium atom, Ge[(4p)²(¹D₂)], 0.883 eV (1 eV ≈ 1.602 18 × 10^–19 J) above the (4p)²(³P_J) ground state. The ¹D₂ atom was generated from the pulsed irradiation (λ≳ 160 nm) of both GeCl₄ and Ge(CH₃)₄ in the presence of an excess of helium gas and the added reactant gases in a slow-flow system, kinetically equivalent to a static system. This was then monitored photoelectrically by time-resolved atomic resonance absorption spectroscopy in the ultraviolet using the resonance transition at λ= 241.737 nm {Ge[(4d)²(¹D⁰₂)]â†�[(4p)¹(¹D₂)]} and employing direct computer interfacing and signal averaging. Ge(CH₃)₄ was found to yield the higher densities of the ¹D₂ state following photolysis and was normally employed as the photochemical precursor with added reactants through GeCl₄ could also be used for quenching studies. The following absolute second-order rate constants [k_R/cm³ molecule^–1 s^–1(300 K)] for the removal of Ge(4 ¹D₂) with various collision partners (R) are reported: GeCl₄, (2.7 ± 0.1)× 10^–10; Ge(CH₃)₄, (4.2 ± 0.2)× 10^–10; H₂, (8.3 ± 0.4)× 10^–11; D₂, (6.9 ± 0.3)× 10^–11; Xe, (2.0 ± 0.1)× 10^–12; He, <3.6 × 10^–16. These results constitute the first reported body of second-order absolute rate data for the collisional removal of Ge(4 ¹D₂), to the best of our knowledge. The resulting rate data are considered in the context of Group 14 atoms in the low-lying (np)²(¹D₂, ¹S₀) metastable states in terms of the nature of the potential surfaces involved on collision on the basis of the weak spin–orbit coupling approximation and (J,Ω) coupling and analogous collisional data for Ge[(4p)²(¹S₀)](E= 2.029 eV) reported hitherto from studies in the ‘single-shot mode’.