2004ApJ...617..384R

We have surveyed the high-mass Galactic star-forming regions G19.61-0.23, G45.47+0.05, and W75N for interstellar methanol (CH₃OH), formic acid (HCOOH), acetic acid (CH₃COOH), methyl formate (HCOOCH₃), methyl cyanide (CH₃CN), and ethyl cyanide (CH₃CH₂CN) with the Berkeley-Illinois-Maryland Association Array. From our observations, we have detected two new sources of interstellar HCOOH toward the hot core regions G19.61-0.23 and W75N. We have also made the first detections of CH₃CH₂CN and HCOOCH₃toward G19.61-0.23. The relative HCOOH/HCOOCH₃abundance ratio toward G19.61-0.23 is 0.18, which is comparable to the abundance ratios found by Liu and colleagues toward Sgr B2(N-LMH), Orion, and W51 (∼0.10). We have made the first detection of HCOOCH₃toward W75N. The relative HCOOH/HCOOCH₃abundance ratio toward W75N is 0.26, which is more than twice as large as the abundance ratios found by Liu and colleagues. Furthermore, the hot core regions around W75N show a chemical differentiation between the O and N cores similar to what is seen toward the Orion Hot Core and Compact Ridge and W3(OH) and W3(H₂O). It is also apparent from our observations that the high-mass star-forming region G45.47+0.05 does not contain any compact hot molecular core (HMC), and as a consequence its chemistry may be similar to that of cold dark clouds. Finally, the formation of CH₃COOH appears to favor HMCs with well-mixed N and O, despite the fact that CH₃COOH does not contain a N atom. If proved to be true, this is an important constraint on CH₃COOH formation and possibly other structurally similar biomolecules.