Outgassing behavior and composition of comet C/1999 S4 (LINEAR) during itsdisruption

The gas activity of comet C/1999 S4 (LINEAR) was monitored at radio wavelen gths during its disruption. A runaway fragmentation of the nucleus may have begun around 18 July 2000 and proceeded until 23 July. The mass in small i cy debris (less than or equal to 30-centimeter radius) was comparable to th e mass in the Large fragments seen in optical images. The mass budget after breakup suggests a small nucleus (similar to 100- to 300-meter radius) tha t had been losing debris for weeks. The HNC, H2CO, H2S, and CS abundances r elative to H2O measured during breakup are consistent with those obtained i n other comets. However, a deficiency in CH3OH and CO is observed.