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LaO emission bands of the green-yellow, red, and near infra red region of the spectrum were analysed. Part of the scope of this contribution is to report some neglected information given in publications on this subject by other authors. For instance, an extra branch of important intensity in the green-yellow system of $La16O$, and some “jumps” in the position of another two branches strongly suggest that further developments are still needed to resolve the structure of this molecule without ambiguity, in spite of recent trends supported by analogy with related molecules (i.e. ScO). The bands of $La18O$ were obtained in an are at reduced pressure. Preliminary analysis of lines belonging to branches without irregularity confirm the rotational assignment given for lines of same character in the $La16O$ band specturm. Also rotational constants have been calculated for the isotopic molecule. For the lower common electronic level involved we found $Bo\prime \prime =0.3116$.