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A complex emission spectrum in the 440–550 nm region has been recorded by bombarding targets of Al2O3 (and Al under low O2 partial pressure) polycrystalline surface with fast (5 keV) Kr+ ion beams under high vacuum (10−8 Torr). This spectrum has been compared with the chemiluminescence spectrum of AlO formed by laser ablation of an Al target in the presence of oxygen. Both spectra exhibit strong Al lines, weak Al+ lines and very weak molecular features, among which bandheads of the Δv=0,±1,±2 sequences of the AlO B2Σ+–X2Σ+ system have been identified. The internal energy distribution of the AlO B state, determined by simulation of the B–X system, shows that both techniques yield highly vibrationally and rotationally excited AlO molecules in the B state. Local equilibrium is achieved ( T rot =T vib ≃4000 K ) for the B2Σ+ state of AlO formed via laser ablation, in agreement with previous studies and with a reaction scheme proceeding through a long-lived intermediate. In contrast, the AlO molecules formed in the B2Σ+ state through fast ion beam bombardment are much more rotationally than vibrationally excited. The rovibronic population distributions, most probably highly non-thermal, can be roughly represented by thermal populations corresponding to rotational and vibrational temperatures of 13 000 and 5000 K, respectively. |
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