Depletion kinetics of chromium atoms by sulfur dioxide

The gas-phase depletion kinetics of Cr(a(7)S(3), a(5)S(2), a(5)D(J)) in the presence of SO2 are reported. Chromium atoms were produced by the 248 nm p hotodissociation of chromium carbonyl and were detected by laser-induced fl uorescence. The ground state of Cr, a(7)S(3), was found to react rapidly vi a a termolecular mechanism with SO2. At 297 K, the limiting low-pressure th ird-order rate constant is k(o) = (2.68 +/- 0.41) x 10(-28) cm(6) molecule( -2) s(-1), and the limiting high-pressure second-order rate constant is k(i nfinity) = (2.73 +/- 0.38) x 10(-10) cm(3) molecule(-1) s(-1); the uncertai nties represent +/-1 sigma in precision. k(0) was found to decrease with in creasing temperature. The binding energy of CrSO2 is estimated at 53 kcal m ol(-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 x 10(-10) cm(3) molecule(-1) s(-1), and the a(5)D(J) spin/orbit sta tes depleted at the collision rate of 2.97 x 10(-10) cm(3) molecule(-1) s(- 1); overall uncertainties are estimated at less than or equal to 35%. Both chemical and physical quenching are likely for the excited states. The pres ent work completes a study on the depletion kinetics of group 6 transition metal atoms by SO2. Results are interpreted in terms of long-range attracti ve forces between Cr and SO2 and the orbital occupancies of the Cr atomic s tates.