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A multitransitional study with the BIMA interferometric array was carried outtoward the starless core found in the L673 region, in order to study thesmall-size structure of the cores detected with previous single--dishobservations, which provides us with a test of the predictions of the chemicalmodel of Taylor et al. (1996; 1998). We detected emission in the CS (2-1), N2H+(1-0), and HCO+ (1-0) lines. Several clumps of size ~0.08 pc were found foreach line distributed all over the region where previous single-dish emissionwas found (Morata et al. 1997). Each molecular transition traces differentlythe clump distribution, although in some cases the detected clumps arecoincident. The distribution of the N2H+ emission and the single-dish NH3emission are coincident and compatible with an origin in the same gas. Thelarge fraction of missing flux measured for the CS (2-1) transition can beexplained if the cloud is formed by a clumpy and heterogeneous medium. Fourpositions were selected to derive the abundance ratios [N2H+/CS] and [HCO+/CS]from the molecular column density determinations, and to compare them with thevalues predicted by the chemical model. The model was able to explain theinterferometric observations, and, in particular, the chemical differentiationof the detected clumps and the coincidence of the NH3 and N2H+ emissions. Thelack of HCO+ towards the two selected positions that trace the more evolvedclumps cannot be accounted for by the model, but it is possibly due to strongself-absorption. We propose a classification of the studied clumps according tothe stage of chemical evolution indicated by the molecular abundances.Comment: 10 pages, 9 figures, accepted for publication in A&

Multitransitional observations of the CS core of L673