Comparative chemistry of diffuse clouds - V. Ammonia and formaldehyde

Using the VLA and NRAO 140' telescopes we observed the lambda 1.3 cm (1, 1) and (2, 2) lines of NH(3) in absorption and emission toward the compact extragalactic continuum sources NRAO150 (B0355+508) and 3C 111 (B0415+379). These sources are occulted by some seven local diffuse and translucent clouds showing molecular absorption in OH, CO, HCO(+) and C(2)H: for the four features having NH(3) absorption, we find rotational excitation temperatures 18-24 K, suggesting kinetic temperatures of at least 25-30 K. The abundance ratio N(NH(3))/N(HCO(+)) is comparable to values quoted for the cyanopolyyne peak in TMC-1 (i.e., 2.5) in three of four cases where NH(3) was seen. For clouds with higher column density N(HCO(+)) greater than or similar to 10(12) cm(-2), the NH(3) column density N(NH(3)) is well correlated only with N(CS) ([N(NH(3))/N(CS)] approximate to 1.0) and N(H(2)CO) ([N(NH(3))/N(H(2)CO)] approximate to 0.4). N(H(2)CO) is well correlated with N(NH(3)) and N(CS) ([N(H(2)CO)/N(CS)] approximate to 2.3) and the H(2)CO abundance relative to other species is like TMC-1, with ([N(H(2)CO)/N(HCO(+))] approximate to 2.3).