Observations are presented of the J = 1 --> 0 line of HCN toward P/Swi
ft-Tuttle 1992t with the NRAO 12 m telescope on 2, 3 and 31 December 1
992, and of the J = 3 --> 2 line on 30 December 1992. Upper limits wer
e obtained for the 1(10)-1(11) transition of HDO. We measure an HCN pr
oduction rate Q(HCN) = (2.9 +/- 1.0) x 10(26) s-1 on 31 December 1992.
A cometary water ice [D]/[H] ratio < 2.5 x 10(-3) is inferred from th
e HDO upper limit.