A MOLECULAR LINE SURVEY OF SAGITTARIUS-B2 AND ORION-KL FROM 70 TO 115 GHZ .2. ANALYSIS OF THE DATA

The NRAO 3 mm survey has observed over 800 lines in OMC-1 and over 700 in Sgr B2. Detailed abundance analyses have been made for 36 species in Sgr B2 and 27 in OMC-1 for which between four and 98 transitions have been observed per species. In most cases the LTE "rotational diagram" method is used, while LVG radiative transfer analyses are used in addition for species whose cross sections are known. The derived abundances agree well with those of all 20 species analyzed in the BTL Sgr B2 survey and all 11 species analyzed in the Onsala OMC-1 survey, especially when differences in beam sizes are accounted for. Limitations of the LTE optically thin approach are emphasized, the most striking of which is the failure to account for the anomalously strong emission from intrinsically weak transitions in all the most complex species (CH3OHCO, (CH3)2O, CH3CHO, EtOH, NH2CHO, CH2CHCN, EtCN). Either large opacities or pumping effects are implicated. Arguments based on the patterns of such transitions, as well as detailed excitation calculations employing of order 100 levels for three of the species, suggest large opacities at least for CH3OHCO, (CH3)2O, CH3CHO, and EtOH, and possibly for all cases. Abundances must in this case be revised upward by factors of 10-300, posing severe problems for current gas phase chemical models, and suggesting a major role for grain chemistry for these species. The intensity and abundance ratios of the existing 3 mm surveys of Sgr B2 (NRAO, BTL) and OMC-1 (NRAO, Onsala) are compared to deduce the relative contributions to the emission of each molecular species from compact, hot sources and from extended, cool regions. The results are consistent with those deduced from kinematic information in the case of OMC-1, but not for Sgr B2 for which we conclude that the kinematics are far more complex than currently recognized. Based on the relative contributions from compact, hot sources and extended cool regions for both Sgr B2 and OMC-1, and on what is known of their morphologies, it is concluded that the chemistries of the two regions are more similar than previously thought, suggesting a similar cosmic-ray flux, evolutionary stage, and elemental abundance distribution. While it has been known that OMC-1 is chemically distinct from objects like TMC-1 (no massive star formation, possibly chemical non-steady state, possibly carbon-rich) and the circumstellar shell IRC 10216 (thermochemical equilibrium and photochemistry, carbon-rich), it has not previously been recognized that at least two most prominent massive star-forming regions, both O-rich but of very different size and location in the Galaxy, may have indistinguishable chemistries.