A mixture of NO and water vapor was ionized inside a chamber using an EUV source to produce cluster ions. Ion-cluster formation started within a minute but the time for attaining peak concentration for different ions varied from 1 min to 40 min. New findings here are ( a) the detection of higher order clusters of proton and NO+ hydrates (109(+), 127(+) and 102(+)) and (b) that the concentration of most of the hydrated ions showed oscillatory behavior. Other positive ions detected were 33(+), 54(,)(+) 66(+), 71(+), 76(+), 83(+), 86(+), 93(+), 94(+), 112(+), 117(+), 131(+) ( with high concentration) and 19(+), 29(+) and 37(+) ( with low concentrations). Effect of lower and upper thresholds of chamber pressure, for the production of cluster ions was observed. These pressure thresholds correspond to an altitude range of 50 to 100 km in the ionosphere, where cluster ions have been observed.