2002ApJ...576..264R

We have detected interstellar acetic acid (CH₃COOH) toward the hot core source W51e2. This is the first new source of interstellar CH₃COOH since its discovery by Mehringer et al. toward the hot core source Sgr B2(N-LMH). In this paper, we report CH₃COOH observations at two new frequencies toward Sgr B2(N-LMH) with the OVRO array and at 10 frequencies toward W51e2 with the Berkeley-Illinois-Maryland Association array. Toward Sgr B2(N-LMH) the agreement in positions, intensities, and velocities between the two lines from the previous study and the two new lines strongly indicates that all four CH₃COOH lines are coming from a common source. Using all four detected transitions, we find an average column density of 6.1(6)x10¹⁵ cm^–2, a fractional abundance of (0.8-6)x10^–10 relative to H₂ and (3-6)x10^–2 relative to its isomer methyl formate (HCOOCH₃). Toward W51e2, we find a CH₃COOH column density of 1.7(5)x10¹⁶ cm^–2 with a fractional abundance of 1.7x10^–9 relative to H₂ and (1-6)x10^–2 relative to HCOOCH₃. Furthermore, we find the distribution of CH₃COOH toward W51e2 is coincident with HCOOCH₃, thus suggesting a similar formation mechanism.