The Molecular Condensations Ahead of Herbig-Haro Objects. I. Multi-transition Observations of HH 2

We present a CSO and BIMA molecular line survey of the dense, quiescent molecular environment ahead of HH2. The molecular gas is cold, 13 K, and moderately dense, 3x10^5 cm^-3. A total of 14 species has been detected (including different isotopes and deuterated species). The relative abundances of the clump are compared with other dense molecular environments, including quiescent dark clouds, and active low and high mass star forming regions. This comparison confirms the peculiar chemical composition of the quiescent gas irradiated by the HH objects. Thus, from this comparison, we found that the HCO+, CH3OH and H2CO are strongly enhanced. SO and SO2 are weakly enhanced, whereas HCN and CS are underabundant. The CN abundance is within the range of value found in starless dark clouds, but it is low with respect to high mass star forming regions. Finally, the chemical composition of HH2 confirms the qualitative results of the Viti & Williams (1999) complex chemical model that follows the chemical behavior of a molecular clump irradiated by a HH object.