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We aim to determine the production rates of several parent and productvolatiles and the 12C/13C isotopic carbon ratio in the long-period comet C/2004Q2 (Machholz), which is likely to originate from the Oort Cloud. The lineemission from several molecules in the coma was measured with highsignal-to-noise ratio in January 2005 at heliocentric distance of 1.2 AU bymeans of high-resolution spectroscopic observations using the SubmillimeterTelescope (SMT). We have obtained production rates of several volatiles (CH3OH,HCN, H13CN, HNC, H2CO, CO and CS) by comparing the observed and simulatedline-integrated intensities. Furthermore, multiline observations of the CH3OH(7-6) series allow us to estimate the rotational temperature using the rotationdiagram technique. We find that the CH3OH population distribution of the levelssampled by these lines can be described by a rotational temperature of 40 \pm 3K. Derived mixing ratios relative to hydrogen cyanide areCO/CH3OH/H2CO/CS/HNC/H13CN/HCN = 30.9/24.6/4.8/0.57/0.031/0.013/1 assuming apointing offset of 8" due to the uncertain ephemeris at the time of theobservations and the telescope pointing error. The measured relative molecularabundances in C/2004 Q2 (Machholz) are between low- to typical values of thoseobtained in Oort Cloud comets, suggesting that it has visited the inner solarsystem previously and undergone thermal processing. The HNC/HCN abundance ratioof ~3.1% is comparable to that found in other comets, accounting for thedependence on the heliocentric distance, and could possibly be explained byion-molecule chemical processes in the low-temperature atmosphere. From atentative H13CN detection, the measured value of 97 \pm 30 for the H12CN/H13CNisotopologue pair is consistent with a telluric value.

Submillimetric spectroscopic observations of volatiles in comet C/2004 Q2 (Machholz)