2006A&A...448..253L

Using the VLA and NRAO 140' telescopes we observed the λ1.3cm (1, 1) and (2, 2) lines of NH₃ in absorption and emission toward the compact extragalactic continuum sources NRAO150 (B0355+508) and 3C111 (B0415+379). These sources are occulted by some seven local diffuse and translucent clouds showing molecular absorption in OH, CO, HCO⁺ and C₂H: for the four features having NH₃ absorption, we find rotational excitation temperatures 18-24K, suggesting kinetic temperatures of at least 25-30K. The abundance ratio N(NH₃)/N(HCO⁺) is comparable to values quoted for the cyanopolyyne peak in TMC-1 (i.e., 2.5) in three of four cases where NH₃ was seen. For clouds with higher column density N(HCO⁺)>10¹²cm^–2, the NH₃ column density N(NH₃) is well correlated only with N(CS) (<N(NH₃)/N(CS)≥∼1.0) and N(H₂CO) (<N(NH₃)/N(H₂CO)≥∼0.4). N(H₂CO) is well correlated with N(NH₃) and N(CS) (<N(H₂CO)/N(CS)≥∼2.3) and the H₂CO abundance relative to other species is like TMC-1, with (<N(H₂CO)/N(HCO⁺)≥∼2.3).