Temperature-dependent studies of the reaction of W(a 5D J , a 7S3) with O2

Abstract

The gas-phase reactivities of W(a 5D,, a 7S3) with O2 in the temperature range 298-573 K are reported. Tungsten atoms were produced by the photodissociation of W(CO), and detected by laser-induced fluorescence. The disappearance rate constant of the s1d5 a ' S , state is of the order of the gas kinetic rate constant. The removal rate constants for the s2d4 a 5D, states are J dependent. The a 5D, states are not as reactive as the s1d5 a 'S3 state and are found to be temperature dependent. The disappearance rates of all states in the presence of O2 are found to be pressure independent with buffer gas. Physical quenching rate constants for the excited states in the presence of Ar, He, N, and sF6 are also reported. Results are discussed in terms of the different electron configurations of the states.

Depletion kinetics of low-lying states of tungsten in the presence of NO, N2O, and SO2

“…The other possible interpretation is electronic relaxation to a Boltzmannized distribution of the W states followed by removal due to chemical reaction/physical quenching. This latter interpretation was rejected due to the lack of observing the concomitant growth in the a 5 D 0 and/or a 5 D 1 states expected if physical quenching were associated with 1 .…”

“…For the a 7 S 3 state, helium was used as the buffer gas since argon quenches the a 7 S 3 state very quickly [1]. Helium (7)).…”

“…Chemical reaction is obviously the only available removal process for the a 5 D 0 ground state, but physical quenching is a possible removal channel for the a 5 D 1 and a 7 S 3 states. The conditions in this work are nearly identical to those in the W ϩ O 2 work [1]; i.e., similar precursor partial pressures and photolysis fluences were used. Thus, the initial relative populations of the different states of tungsten following photodissociation of W(CO) 6 were of the same order of magnitude as in Two mechanisms for the oxidation of transition metal atoms have been proposed and discussed in detail.…”

“…The experimental apparatus used in these experiments has been discussed in detail previously [1,2] and is only briefly described here. The experiments were performed under pseudo-first-order kinetics ([W] Ͻ Ͻ [Ox]) using a laser-photolysis/laser-induced fluorescence (LIF) technique in an apparatus with slowly flowing gas.…”

“…A small amount of SF 6 was added to the reaction chamber as a buffer in addition to the Ar for the a 5 D 1 experiments (SF 6 accounted for Ϸ 10% of the total pressure); SF 6 quickly quenches the states lying above the a 5 D 1 state [1]. The result is short lived growth at the beginning of the runs similar to those experiments with N 2 O for the same state.…”