Depletion Kinetics of Niobium Atoms in the Gas Phase

The gas phase depletion kinetics of Nb(a 6 D J,a 4 F J ) in the presence of O 2, SO 2, CO 2, N 2 O, and NO are reported. Niobium atoms were produced by the 248 nm photodissociation of Nb(C 5 H 5 )(CO) 4 and detected by laser-induced fluorescence. The ground term of Nb(4d 4 5s 1 a 6 D J ) reacts at or above the collision rate with all of the aforementioned oxidants. The first excited term, Nb(4d 3 5s 2 a 4 F J ), is not as reactive with these oxidants. Results are interpreted in terms of long-range attractions and valence interactions. Additionally, we report reaction rate constants for ground state Nb interacting with N 2, CH 4, and SF 6 . Nb(a 6 D J ) is unreactive toward CH 4 . Nb(a 6 D J ) + N 2 is pressure dependent at 297 K with k 0 = (2.6 ± 0.3) × 10 -32 cm 6 s -1 and k ∞ = (4.1 ± 0.5) × 10 -13 cm 3 s -1 . Nb(a 6 D J ) + SF 6 is temperature dependent with the rate constants given by k ( T ) = (1.2 ± 0.3) × 10 -10 exp[−(4.8 ± 0.2) kcal mol -1 / RT ] cm 3 s -1 . Depletion of the a 4 F J term by N 2, SF 6, and CH 4 is J -dependent.