The collisional behaviour of electronically excited germanium atoms, Ge(4p 2( 1D 2)), with simple molecules investigated by time-resolved atomic resonance absorption spectroscopy in the UV

Abstract

The collisional behaviour is presented of electronically excited germanium atoms, Ge(4p 2( 1D 2)), 0.883 eV above the 4p 2( 3P J ) ground state, in the presence of a range of simple molecules. We have shown that the 1D 2 atom, which is optically metastable, may be produced photochemically in the pulsed mode and monitored by time-resolved atomic resonance absorption spectroscopy in the UV. The electronically excited germanium atoms are normally generated from the low-wavelength pulsed irradiation (γ ≳ 160 nm) of Ge(CH 3) 4 in the presence of excess helium gas and added reactant gases in a slow flow system, kinetically equivalent to a static system. This photochemical precursor yields higher densities of Ge(4 1D 2) for kinetic studies than GeCl 4 which is also used. The electronically excited atom was monitored photoelectrically in the repetitive mode by time-resolved atomic resonance absorption spectroscopy in the UV with direct computer interfacing for data capture and analysis. Ge(4 1D 2) was monitored using the resonance transition at γ = 241.737 nm (Ge(4d( 1D 2)) ← (4p 2( 1D 2))). The following absolute second-order rate constants ( k R, errors 2σ) are reported for the collisional removal of Ge(4 1D 2) with various collision partners (R): ▪ The resulting rate data are compared with analogous collisional data for Ge(4p 2( 1S o)) ( E=2.029 eV) reported from studies in the single-shot mode. In all cases, collisional removal of the 1D 2 state is significantly faster than the 1S 0 state. The rate data are also considered in the context of Group IV atoms in the low-lying np 2( 1D 2, 1S 0) 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.