A three-position spectral line survey of sagittarius B2 between 218 and 263 GHz. II. Data analysis

We present an analysis of the data from our Swedish-ESO Submillimetre Teles cope molecular line survey in the 1.3 mm band of the N, M, and NW positions in the Sgr B2 molecular cloud. The line emissions from 42 molecular specie s, and some of their isotopomers, were analyzed assuming a single temperatu re and a homogeneous source. In cases where a source size much smaller than the antenna beam (23 ") could he estimated, optical depth effects were als o accounted for. In this way rotation temperatures, molecular column densit ies, and in several cases also source sizes, were determined. Observed and modeled intensities are presented in rotation diagrams. A few complex molec ular species, NH2CHO, CH3CHO, C2H3CN, C2H5CN, and CH3OCHO, mainly in the N source, exhibit anomalously strong intensities in their intrinsically weak b- and c-type lines. We argue that this effect can hardly be explained by h igh optical depths alone, and therefore propose that the possibility of rad iative pumping via the low-lying vibrational states of these molecules shou ld be investigated as an alternative explanation. The highest rotation temp eratures, up to about 500 K, were found for large molecules toward Sgr B2(N ), closely followed by Sgr B2(M). In Sgr B2(NW), which samples the cloud en velope, the rotation temperatures are 15-50 K. For molecules with too few o bserved transitions to allow determination of rotation temperatures, the co lumn density was calculated assuming optically thin emission, and we adopte d rotation temperatures of 50, 50, and 20 K in M, N, and NW, respectively. Column density ratios of isotopomers were determined. After a critical disc ussion of the resolution-dependent H-2 column density toward the observed p ositions, abundances relative to H-2 were calculated. We discuss the chemic al differences between the three observed cloud positions and compare with the hot core, compact ridge, and outflow in Orion A. Hot core-type molecule s like CH2NH, NH2CN, CH3CN, C2H3CN, and C2H5CN, as well as H2CS, are more a bundant in Sgr B2(N) by factors of 3-8 as compared to the M position. Large oxygen-containing species like CH3OH, CH3CHO, CH3OCHO, CH3OCH3, and NH2CHO , of compact ridge-type, show similar or slightly enhanced abundances in N as compared to M. The C2H5OH abundances are similar in N, M, and also in NW . The SO2 and SO abundances in the M core (4 x 10(-7) and 1 x 10(-7), respe ctively) are 13 and 5 times higher than in N and are very enhanced (10(3) a nd 10(2) times) as compared to NW. Such high SO, and SO abundances are also found in the prominent Orion A outflow source. In M the (SOO)-O-18 and (SO )-O-18 data suggest a O-16/O-18 ratio of 120. The HOCO+ ion is detected in all three positions and appears to be 3 times more abundant in the NW posit ion. HCNH+ is seen only in NW.