The effect of carbonyl complexation on highly exothermic vanadium oxidation reactions

The effects of CO complexation on highly exothermic vanadium oxidation reac tions is evaluated. We study the chemiluminescent (CL) reaction products fo rmed when vanadium vapor entrained in Ar or CO is oxidized by O-3 or NO2. T he multiple collision V + Ar + O-3 --> VO*(C(4)Sigma(-), (4)Phi, X-2) + Ar + O-2 reactive encounter yields two previously unreported VO excited states , whereas the V + Ar + NO2 --> VO* + Ar + NO reactive encounter populates s tates up to and including VO* C(4)Sigma(-). The multiple collision V + nCO + O-3 reactive encounter would appear to form a VOCO excited state complex, emitting in the region 420-560 nm, via the formation and oxidation of V(CO )(2) viz. V(CO)(2) + O-3 --> VOCO* + CO + O-2 and a relaxed VO excited stat e emitter via V + nCO + O-3 --> VO* + nCO + O-2 where the VO excited state excitation is mediated by V-CO complexation. In complement, the much less e xothermic VNO2 encounter displays an emission which, in concert with previo us studies of CO complexation, suggests the formation of a VO(CO)(2) excite d state complex viz. V(CO)(2) + NO2 --> VO(CO)(2)* + NO. The experiments ch aracterizing CL are complemented by comparative laser-induced fluorescence studies of the VO X(4)Sigma(-)-CO and Ar interactions and their influence o n the VO C(4)Sigma(-)-X(4)Sigma(-) laser-induced excitation spectrum. These studies, in conjunction with further attempts to excite LIF in the 420-560 nm region, suggest that the observed complex emissions result primarily fr om VO excited state interactions. Complementary time-of-flight mass spectro scopy of vanadium and vanadium-oxide-carbonyl complex formation demonstrate s the formation of V(CO), V(CO)(2), V-2(CO), and VOCO, the latter three of which demonstrate clear metastable-ion dissociation peaks for the processes VOCO+ --> V+ + CO2, V(CO)(2)(+) --> V+ + 2CO, and V-2(CO)(+) --> V-2(+) CO, suggesting that these vanadium complexes when formed in a reaction-base d environment may be photodissociated with light in the visible and ultravi olet regions. (C) 2000 Elsevier Science B.V. All rights reserved.