Depletion Kinetics of Chromium Atoms by Sulfur Dioxide

Abstract

The gas-phase depletion kinetics of Cr(a 7 S 3 , a 5 S 2 , a 5 D J ) in the presence of SO 2 are reported. Chromium atoms were produced by the 248 nm photodissociation of chromium carbonyl and were detected by laser-induced fluorescence. The ground state of Cr, a 7 S 3 , was found to react rapidly via a termolecular mechanism with SO 2 . At 297 K, the limiting low-pressure third-order rate constant is k o ) (2.68 ( 0.41) × 10 -28 cm 6 molecule -2 s -1 , and the limiting high-pressure second-order rate constant is k ∞ ) (2.73 ( 0.38) × 10 -10 cm 3 molecule -1 s -1 ; the uncertainties represent (1σ in precision. k o was found to decrease with increasing temperature. The binding energy of CrSO 2 is estimated at 53 kcal mol -1 from combining the kinetic results with unimolecular rate theory and density functional theory. Cr(a 5 S 2 ) depleted with a rate constant of k ) 6.32 × 10 -10 cm 3 molecule -1 s -1 , and the a 5 D J spin/orbit states depleted at the collision rate of 2.97 × 10 -10 cm 3 molecule -1 s -1 ; overall uncertainties are estimated at e35%. Both chemical and physical quenching are likely for the excited states. The present work completes a study on the depletion kinetics of group 6 transition metal atoms by SO 2 . Results are interpreted in terms of long-range attractive forces between Cr and SO 2 and the orbital occupancies of the Cr atomic states.

A kinetic study of the reactions of vanadium, iron, and cobalt with sulfur dioxide

“…The experimental arrangement and method are quite similar to what is given in our previous work on other TM þ SO 2 systems. 3 The TM atoms were produced by laser photodissociation of TM compounds and detected by laser-induced fluorescence (LIF). The reaction chamber, contained in a convection oven capable of attaining temperatures up to 623 K, was a stainless steel cross with gas inlet and outlet ports, a viewport for LIF detection, and windows for passage of the laser beams.…”

“…Kinetics studies on the reactions of gas-phase transition metal (TM) species with small oxygen-containing molecules have received considerable attention. [1][2][3][4][5][6][7][8][9][10][11] These studies are of interest because they provide information on catalytic bond activation and aid in the understanding of the reactivities of TM species in atmospheric chemistry. For example, CO 2 , being a potential alternative precursor in organic synthesis, can be catalytically activated by TM centers.…”

“…22,23 There also appears to be a correlation between the reaction efficiency and the promo-tion energy to the lowest state of d nÀ1 s 1 occupancy. 3 Thus, more investigations on these reactions are needed to gain a deeper understanding of how TM atoms interact with SO 2 in the gas phase.…”

“…We recently reported a kinetic study of the association reactions of Cr, Mn, and Ni with SO 2 . 3,5 The efficiencies of these reactions were discussed in terms of the orbital occupancies of the transition metals. Ground state chromium, which has the electron configuration [Ar]3d 5 4s 1 , has a measured room temperature rate constant of (2.68 AE 0.41) Â 10 À28 cm 6 molecule À2 s À1 .…”

Applying a Nonspin-Flip Reaction Scheme to Explain for the Doublet Sulfide Oxides SMO2 Observed for the Reactions of SO2 with V(4F), Nb(6D), and Ta(4F)

“…Kinetic investigations have also been carried out on the reactions of this molecule with different transition metal atoms. Results emerging from those studies show that SO 2 is more reactive than other gases (O 2 , SO 2 , CO 2 , N 2 , N 2 O, and NO) in this kind of reactions [10][11][12][13][14]. e interaction of SO 2 with laser-ablated transition metal atoms in groups IV-VI of the periodic table has been investigated by IR spectroscopy under matrix-isolation conditions [15][16][17].…”