Temperature-dependent rate constants for the reactions of gas-phase lanthanides with O-2

The reactivity of the gas-phase lanthanide atoms Ln (Ln = La-Yb with the ex ception of Pm) with O-2 is reported. Lanthanide atoms were produced by the photodissociation of [Ln(TMHD)(3)] and detected by laser-induced fluorescen ce. For all the lanthanides studied with the exception of Yb, the reaction mechanism is bimolecular abstraction of an oxygen atom. The bimolecular rat e constants (in molecule(-1) cm(3) s(-1)) are described in Arrhenius form b y k[Ce((1)G(4))] = (3.0 +/- 0.4) x 10(-10) exp(-3.4 +/- 1.3 kJ mol(-1)/RT); Pr(I-4(9/2)), (3.1 +/- 0.7) x 10(-10) exp(-5.3 +/- 1.5 kJ mol(-1)/RT); Nd( I-5(4)), (3.6 +/- 0.3) x 10(-10) exp(-6.2 +/- 0.4 kJ mol(-1)/RT); Sm(F-7(0) ), (2.4 +/- 0.4) x 10(-10) exp(-6.2 +/- 1.5 kJ mol(-1)/RT); EU(S-8(7/2)), ( 1.7 +/- 0.3) x 10(-10) exp(-9.6 +/- 0.7 kJ mol(-1)/RT); Gd(D-9(2)), (2.7 +/ - 0.3) x 10(-10) exp(-5.2 +/- 0.8 kJ mol(-1)/RT); Tb(H-6(15/2)), (3.5 +/-. 0.6) x 10(-10) exp(-7.2 +/- 0.8 kJ mol(-1)/RT); Dy(I-5(8)), (2.8 +/- 0.6) x 10(-10) exp(-9.1 +/- 0.9 kJ mol(-1)/RT); Ho(I-4(15/2),), (2.4 +/- 0.4) x 1 0(-10) exp(-9.4 +/- 0.8 kJ mol(-1)/RT); Er(H-3(6)), (3.0 +/- 0.8) x 10(-10) exp(-10.6 +/- 1.1 kJ mol(-1)/RT); Tm(F-2(7/2)), (2.9 +/- 0.2) x 10(-10) ex p(-11.1 +/- 0.4 kJ mol(-1)/RT), where the uncertainties represent +/-2 sigm a. The reaction barriers are found to correlate to the energy required to p romote an electron out of the 6s subshell. The reaction of Yb(S-1(0)) with O-2 reacts through a termolecular mechanism. The limiting low-pressure thir d-order rate constants are described in Arrhenius form by k(0)[Yb(S-1(0))] = (2.0 +/- 1.3) x 10(-28) exp(-9.5 +/- 2.8 kJ mol(-1)/RT) molecule(-2) cm(6 ) s(-1).