Formation of Electronically Excited Mn sub x O From the Oxidation of Small Manganese Clusters

The chemiluminescent reactions of Mn atoms and clusters with ozone have been studied under multiple-collision conditions. Manganese atoms entrained in room-temperature Ar or helium react with ozone to form the lowest lying MnO* A exp 6 Sigma exp + excited electron state (Mn + O sub 3 + Ar(He) - > MnO*(A exp 6 Sigma exp + ) + O sub 2 + Ar(He)), producing a strong chemiluminescent signal corresponding to the MnO A exp 6 Sigma exp + -X exp 6 Sigma exp + band system. A high flux of Mn vapor is entrained in liquid N sub 2 cooled Ar to induce clustering. This entrained mixture subsequently reacts with ozone to produce a new complex emission system (accompanies MnO A-X system) containing at least 72 bands and extending from 720-970 nm. The new system, which is not present when the carrier gas is not cooled, increases precipitously with entrain gas cooling and increased metal flux. The observed bands are fit within experimental error by the expression nu sub upsilon 1', upsilon 1", upsilon 3', upsilon 3" = 12512 + 600 upsilon sub 1' -534 upsilon sub 1" + 360 upsilon sub 3' --306 upsilon sub 3" , where all values are in cm exp --1 . The ground-state spacing of 306 cm exp --1 is assigned as a Mn--Mn stretch. The 534 cm exp --1 spacing is assigned to a MnO stretch, and the emitting molecule is believed to the asymmetrical Mn--Mn--O isomer. The Mn--Mn stretch frequency is in excellent agreement with a frequency estimated for Mn exp + sub 2 by averaging the derived force constants for Mn sub 2 and Cr sub 2 . The MnO stretching frequency is considerably lower than the 840 cm exp --1 diatomic frequency, lying intermediate to those of KO (384 cm exp --1 ) and CaO (733 cm exp --1 ). This suggests that the bonding in this molecule is similar to the bonding in the alkali-metal oxides and that it may reasonably be represented as (Mn--Mn) exp + O exp -- . Spectra. 19 ref.--AA