Spectroscopic observations of comet C/1999 H1 (Lee) with the SEST, JCMT, CSO, IRAM, and Nancay radio telescopes

Coordinated spectroscopic radio observations of comet C/1999 H1 (Lee) were undertaken between 1999 May 4 and 1999 October 26, using the Swedish-ESO Su bmillimetre Telescope, the James Clerk Maxwell Telescope, the Caltech Submi llimeter Observatory, the 30 m telescope of the Institut de Radio Astronomi e Millimetrique, and the Nancay radio telescope. We report on observations of OH, HCN, CH3OH, H2CO, and CS and on the evolution of their production ra tes with heliocentric distance between 0.8 and 1.7 AU, where the total outg assing rate ranged between 0.2 and 1.6 x 10(29) molecules s(-1). HNC was de tected unexpectedly in this medium-activity comet with a relatively large H NC/HCN mixing ratio of 12%, close to that measured in comet C/1995 O1 (Hale -Bopp), which cannot be explained by current chemical models of the coma. C O was tentatively detected with a low abundance around 4% relative to water and is clearly underabundant in comparison to that in comets Hyakutake and Hale-Bopp. An upper limit of D/H less than 300 x 10(-5) in water was found from a brief search for HDO. Molecular abundances relative to water of the other species around 1 AU are similar to those observed in other comets, a lthough CH3OH (4%) and H2CO (1%) exhibit some of the largest abundances com pared with previous comets.