Depletion Kinetics of Mo(a⁷S₃,a⁵S₂,a⁵D_J) by N₂, SO₂, CO₂, N₂O, and NO

Abstract

The gas phase collisional disappearance of Mo(a 7 S 3 ,a 5 S 2 ,a 5 D J ) in the presence of N 2 , SO 2 , CO 2 , N 2 O, and NO over the temperature range 294-621 K and in the total pressure range 10-600 Torr is reported. Mo atoms were produced by the 248 nm photodissociation of Mo(CO) 6 and MoCl 4 and detected by laser-induced fluorescence. The room temperature depletion rate constant of Mo(a 5 S 2 ) + N 2 is (2.3 ( 0.7) × 10 -11 cm 3 s -1 ; the depletion rate constants of the a 5 D J are smaller and range from (16 ( 8) × 10 -12 for Mo(a 5 D 0 ) to (0.13 ( 0.04) × 10 -12 cm 3 s -1 for the other spin-orbit states. The depletion rate of all states of Mo by SO 2 are on the order of the collision rate. Mo(a 7 S 3 ) is found to be unreactive toward CO 2 , and the rate constant for the reaction of Mo(a 7 S 3 ) with N 2 O is expressed as k(T) ) (2.0 ( 0.5) × 10 -10 exp[-(9.8 ( 0.3) kcal mol -1 /RT] cm 3 s -1 . Termolecular kinetics are observed for Mo(a 7 S 3 ) + NO with k 0 ) (2.6 ( 0.3) × 10 -29 cm 6 s -1 , k ∞ ) (5.8 ( 0.5) × 10 -11 cm 3 s -1 , and F c ) 0.72 ( 0.07 at 296 K; the reaction rates for this reaction decrease with increasing temperature. Depletion rate constants of the reactions of the excited states of Mo with CO 2 , N 2 O, and NO are on the order of 10 -12 -10 -10 cm 3 s -1 ; the depletion kinetics are complex and involve significant energy transfers. Results indicate that the electron configuration of Mo plays a role in its depletion kinetics. In all cases, Mo(4d 5 5s 1 a 5 S 2 ) depletes faster than Mo(4d 4 5s 2 a 5 D J ). The inefficient reactions of Mo(a 7 S 3 ) with CO 2 and N 2 O are attributed to the production of spin-forbidden states.

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

“…In this model, activation barriers are calculated by taking into account the ionization potential and sp promotion energy of the metal, the electron affinity of N 2 O and the bond energy of the metal oxide product. While this model works well for many main group metals, it does not predict transition metals as well [17,19]. With tungsten, however, the activation energy predicted is only 3 kJ mol Ϫ1 lower than the reported value here.…”

“…character [4]. Experiments with vanadium [6], titanium [3,7], molybdenum [2,17], and niobium [25] have been performed recently which generally support this model.…”

Transitions in Order and Molecularity with Temperature in Gaseous Metal Oxidation Reactions. The Sb-O2 System

“…Moreover, few reactions have been studied over sufficiently wide temperature ranges. In the studies of the Cr/NO at 298 K [10] and Mo/NO from 296Ϫ620 K [45,46] systems termolecular fall-off behavior has been established. Shock tube studies in the 1200Ϫ3000 K have shown abstraction to occur for these reactions [47].…”

Reaction dynamics of Mo + O2 → MoO + O studied by a crossed-beam velocity map imaging technique

“…1 For this reason, a fair amount of kinetic studies have been carried out for reactions of gas-phase neutral transition metal atoms with small oxygen-containing molecules (OX). [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] In several studies, the reaction rate constants for some low-lying electronically excited states 21 have been determined, as well as those for the ground states. 2-7, 11, 14-16 Although the excited states usually showed larger reaction rate constants than the ground states, some studies showed higher reactivities of the ground states, and suggested that the electron configuration plays a more important role than the energy.…”

“…2-7, 11, 14-16 Although the excited states usually showed larger reaction rate constants than the ground states, some studies showed higher reactivities of the ground states, and suggested that the electron configuration plays a more important role than the energy. 15,16 To understand the oxidation reactions of the transition metal atoms, two reaction mechanisms have been proposed. One is a direct oxygen abstraction mechanism.…”