Abstract

The gas-phase ion-molecule reactions of Cr + and Mn + with acetone and acetone-d 6 are studied with a Fourier transform ion cyclotron resonance mass spectrometer. Unimolecular dissociation rates of chemically activated complexes, (M(acetone) +) ∗, are obtained using the continuous ejection method. An inverse isotope effect is found for the Cr +/acetone/acetone-d 6 system with k uni H k uni D ∼0.5 , while the unimolecular dissociation rates are about the same for [MnOC(CH 3) 2 +] ∗ and [MnOC(CD 3) 2 +] ∗. The bond dissociation energies, D°(Cr +−OC(CH 3) 2) = 1.82 ± 0.15 eV, D°(Cr +−OC(CD 3) 2) = 1.62 ± 0.15 eV, D°(Mn +−OC(CH 3) 2) = 1.65 ± 0.15 eV and D°(Mn +−OC(CD 3) 2) = 1.49 ± 0.15 eV, are derived from RRKM modeling with input parameters obtained from ab initio calculations. The radiative association reactions of Cr + with acetone are also examined. The unimolecular dissociation rate constant of (Cr +−OC(CH 3) 2) ∗ , derived from the RA kinetics, is compared with the CE measurement.

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