The electronically chemiluminescent reaction Mn+O-3--> MnO*+O-2 was investigated using a beam-gas configuration. Light from the MnO A (6)Sigma(+)-X (6)Sigma(+) transition was collected by a charge coupled device (CCD) array detector with resolutions of 0.5 and 0.1 nm. The spectrum at lower resolution (500-655 nm) encompassed the Delta upsilon = -3 to +2 sequences, while that at higher resolution (555.5-583.5 nm) encompassed only the Delta upsilon = 0 sequence. These two spectra were separately fitted with a nonlinear least-squares program to obtain vibrational and rotational distributions of the nascent MnO*. The limited vibrational-state coverage of the higher-resolution spectrum made it unrealiable for determining the vibrational state distribution, and it was useful only for characterizing the rotational distribution when upsilon(') = 0. The best-fit vibrational excitation is somewhat less than for the Prior model, but the rotational excitation is considerably greater. A consideration of the electronic structure of reactants and products indicates that principal changes occurring in the chemiluminescent reaction are sigma-electron donation from the sd(z)(2) hybridized Mn orbital to the O-3 lowest unoccupied molecular orbital (LUMO) (2b(1)) and pi-electron backdonation from the O-O 4b(2) orbital to the Mn 3d(pi) orbital. Correlation of the orbitals involved indicates that direct access is allowed to the MnO A (6)Sigma(+)(10 sigma*(1)8 sigma(1)) state. This mechanism favors Mn approach perpendicular to the O-3 plane and suggests that the product's rotational excitation may originate in O-2-OMn repulsion arising from removal of electron density from the slightly bonding 4b(2) orbital of O-3. However, some rotational excitation could also be attributed to conservation of angular momentum arising from a sizable reactive impact parameter. The lack of significant vibrational excitation is a consequence of the short-range nature of the partial charge transfer in this reaction channel.