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

The reactivity of the gas phase lanthanide atoms Ln (Ln=La-Yb with the exce ption of Pm) with CO2 is reported. Lanthanide atoms were produced by the ph otodissociation of [Ln(TMHD)(3)] and detected by laser-induced fluorescence . For all the lanthanides studied with the exception of Yb, the reaction me chanism is bimolecular abstraction of an oxygen atom. The bimolecular rate constants (in molecule(-1) cm(3) s(-1)) are described in Arrhenius form by: k[Ce((1)G(4))]=(3.4 +/- 1.0)x10(-10) exp(-3.5 +/- 1.0 kJ mol(-1)/RT); Pr(I -4(9/2)), (2.5 +/- 0.4)x10(-10) exp(-7.9 +/- 0.7 kJ mol(-1)/RT); Nd(I-5(4)) , (3.3 +/- 0.6)x10(-10) exp(- 12.0 +/- 0.8 kJ mol(-1)/RT); Sm(F-7(0)), (1.7 +/- 0.8)x10(-10) exp(-15.8 +/- 1.8 kJ mol(-1)/RT); Eu(S-8(7/2)), (6.6 +/- 2.3)x10(-10) exp(-39.2 +/- 1.6 kJ mol(-1)/RT); Gd(D-9(2)), (1.1 +/- 0.3)x10 (-10) exp(-5.8 +/- 0.9 kJ mol(-1)/RT); Tb(H-6(15/2)), (1.1 +/- 0.3)x10(-10) exp(-10.8 +/- 1.2 kJ mol(-1)/RT); Dy(I-5(8)), (4.0 +/- 0.7)x10(-10) exp(-3 0.3 +/- 0.7 kJ mol(-1)/RT); Ho(I-4(15/2)), (3.7 +/- 1.1)x10(-10) exp(-33.1 +/- 1.3 kJ mol(-1)/RT); Er(H-3(6)), (5.8 +/- 2.5)x10(-10) exp(-36.9 +/- 2.0 kJ mol(-1)/RT); Tm(F-2(7/2)), (1.1 +/- 0.5)x10(-10) exp(-45.4 +/- 2.3 kJ m ol(-1)/RT) where the uncertainties represent +/- 2 sigma. Yb(S-1(0)) is unr eactive 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.