Internal population distribution of the B state of AlO formed by fast ion beam bombardment or laser ablation of an Al2O3 (Al) surface

A complex emission spectrum in the 440-550 nm region has been recorded by b ombarding targets of Al2O3 (and Al under low O-2 partial pressure) polycrys talline surface with fast (5 keV) Kr+ ion beams under high vacuum (10(-8) T orr). This spectrum has been compared with the chemiluminescence spectrum o f AlO formed by laser ablation of an Al target in the presence of oxygen. B oth spectra exhibit strong Al lines, weak Al+ lines and very weak molecular features, among which bandheads of the Delta nu = 0, +/-1, +/-2 sequences of the AlO B(2)Sigma (+)-X(2)Sigma (+) system have been identified. The int ernal energy distribution of the AlO B state, determined by simulation of t he B-X system, shows that both techniques yield highly vibrationally and ro tationally excited AlO molecules in the B state. Local equilibrium is achie ved (T-rot = T-vib similar or equal to 4000 K) for the B(2)Sigma (+) State of AlO formed via laser ablation, in agreement with previous studies and wi th a reaction scheme proceeding through a long-lived intermediate. In contr ast, the AlO molecules formed in the B(2)Sigma (+) state through fast ion b eam 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 a nd vibrational temperatures of 13 000 and 5000 K, respectively. (C) 2000 El sevier Science B.V. All rights reserved.