M. Drahus, University of California at Los Angeles; Bin Yang, University of Hawaii; and J. Hoge, Joint Astronomy Centre, report the detection of HCN (Hydrogen cyanide) in comet C/2010 X1 on July 30 when at heliocentric distance r = 1.07 AU. Observations between July 30.153 and 30.249 UT at the James Clerk Maxwell Telescope show the J = 4-3 line with area about 0.1 K km/s in antenna temperature scale. Assuming an isotropic production of gas at velocity 0.5 km/s and a Boltzmann distribution of energy levels at 50 K, the derived HCN production rate is 1.5 x 1025 molecules/s, comparable to the mean level measured in comet 103P/Hartley at the same heliocentric distance in late 2010 (Drahus et al. 2011, Ap.J. 734, L4).
http://www.cbat.eps.harvard.edu/iau/cbet/002700/CBET002781.txt (subscription required).