The formation mechanism and stability of silicon oxide clusters observed in the ablation of SiO targets at 266 run were investigated by time-of-flight mass spectrometry, laser-induced fluorescence (LIF), and DFT calculations. Neutral and positively charged Si-n(+/0) and SinOmH0.1+ clusters were identified in the plume, but neutral SinOm could not be observed. The time distribution of SiO in the plume measured by postionization with an ArF laser (Delta lambda approximate to 1 nm, tau approximate to 14 ns) and mass spectrometric detection was compared with that obtained by LIF with narrowband dye laser selective excitation of one specific rovibronic transition in SiO. Postionization leads to a multicomponent distribution that extends up to times near 100 mu s after ablation, whereas LIF measurements obtain time distributions shorter than 20 mu s. DFT calculations of several SinOm0/+ were performed, showing that one photon absorption of the postionization laser makes available low-energy dissociation channels of the neutrals, whereas two photon absorption is required for ionization. DFT calculations were carried Out for stoichiometric H-containing clusters SinOnH+ (n = 1-4). For n = 1,2, the optimized geometries involve bonding of hydrogen to one oxygen atom in the clusters; for n = 3 and 4, the structures containing H-Si bonds are more stable.