Temperature dependent rate constants for the reactions of gas phase lanthanides with CO2

Abstract

The reactivity of the gas phase lanthanide atoms Ln (Ln=La–Yb with the exception of Pm) with CO₂ is reported. Lanthanide atoms were produced by the photodissociation of [Ln(TMHD)₃] and detected by laser-induced fluorescence. For all the lanthanides studied with the exception of Yb, the reaction mechanism is bimolecular abstraction of an oxygen atom. The bimolecular rate constants (in molecule^-1 cm³ s^-1) are described in Arrhenius form by: k[Ce(¹G₄)]=(3.4±1.0)×10^-10 exp(-3.5±1.0 kJ mol^-1/RT); Pr(⁴I_9/2), (2.5±0.4)×10^-10 exp(-7.9±0.7 kJ mol^-1/RT); Nd(⁵I₄), (3.3±0.6)×10^-10 exp(-12.0±0.8 kJ mol^-1/RT); Sm(⁷F₀), (1.7±0.8)×10^-10 exp(-15.8±1.8 kJ mol^-1/RT); Eu(⁸S_7/2), (6.6±2.3)×10^-10 exp(-39.2±1.6 kJ mol^-1/RT); Gd(⁹D₂), (1.1±0.3)×10^-10 exp(-5.8±0.9 kJ mol^-1/RT); Tb(⁶H_15/2), (1.1±0.3)×10^-10 exp(-10.8±1.2 kJ mol^-1/RT); Dy(⁵I₈), (4.0±0.7)×10^-10 exp(-30.3±0.7 kJ mol^-1/RT); Ho(⁴I_15/2), (3.7±1.1)×10^-10 exp(-33.1±1.3 kJ mol^-1/RT); Er(³H₆), (5.8±2.5)×10^-10 exp(-36.9±2.0 kJ mol^-1/RT); Tm(²F_7/2), (1.1±0.5)×10^-10 exp(-45.4±2.3 kJ mol^-1/RT) where the uncertainties represent ±2σ. Yb(¹S₀) is unreactive with CO₂ below 623 K. The reaction barriers are found to correlate to the energy required to promote an electron out of the 6s subshell.