K-band radio observations of comet Hale-Bopp: Detections of ammonia and (possibly) water

K-band radio observations of comet Hale-Bopp (C/1995 O1) were conducted in March/April 1997 at the 100-m Telescope of the Max-Planck- Institut fur Radioastronomie. Emission was firmly detected from the five lowest metastable (J = K) inversion transitions of ammonia. Assuming a thermal distribution for the metastable states of NH3, we derive a rotational temperature of 104 +/- 30 K and an ammonia production rate at perihelion of 6.6 +/- 1.3 x 10(28) s(-1). The updated ammonia-to-water abundance ratio is found to be of the order of 1.0%. We also report a marginal detection of the 6(16)-5(23) transition line of water at lambda = 1.35 cm.