  A partial submillimeter line-survey was performed toward 7 high-mass young
stellar objects (YSOs) aimed at detecting H2CO, CH3OH, CH2CO, CH3CHO, C2H5OH,
HCOOH, HNCO and NH2CHO. In addition, other organic species such as CH3CN have
been observed. The aim is to establish the chemical origin of a set of complex
organic molecules thought to be produced by grain surface chemistry in high
mass YSOs. Rotation temperatures and beam-averaged column densities are
determined. Based on their rotation diagrams, molecules can be classified as
either cold (<100 K) or hot (>100 K). This implies that complex organics are
present in at least two distinct regions. Furthermore, the abundances of the
hot oxygen-bearing species are correlated, as are those of HNCO and NH2CHO.
This is suggestive of chemical relationships within, but not between, those two
groups of molecules. The most likely explanation for the observed correlations
of the various hot molecules is that they are ``first generation'' species that
originate from solid-state chemistry. This includes H2CO, CH3OH, C2H5OH,
HCOOCH3, CH3OCH3, HNCO, NH2CHO, and possibly CH3CN, and C2H5CN. The
correlations between sources implies very similar conditions during their
formation or very similar doses of energetic processing. Cold species such as
CH2CO, CH3CHO, and HCOOH, some of which are seen as ices along the same lines
of sight, are probably formed in the solid state as well, but appear to be
destroyed at higher temperatures. A low level of non-thermal desorption by
cosmic rays can explain their low rotation temperatures and relatively low
abundances in the gas phase compared to the solid state. The CH3CCH abundances
can be fully explained by low temperature gas phase chemistry. No cold
N-containing molecules are found.
