March 2005

Thioformaldehyde

The initial detection of thioformaldehyde (H2CS) was reported in 1973 by Sinclair et al. The 2(11)-2(12) microwave transition at 3139.38 MHz was observed in Sgr B2 with the Parkes Observatory 64 meter telescope in New South Wales, Australia. This was the first interstellar species detected "by a group outside the USA." The Parkes facility may be the only radio telescope in the world to be the subject of a major motion picture (The Dish) due to its role in bringing images from the historic Apollo 11 moonwalk to the world.

One of the co-discoverers of thioformaldehyde, Nicholas Fourikis, recalls a technical problem that nearly curtailed their observations: "The phase-lock subsystem of the 9cm receiver we used was inoperative. Without phase-locking of the receiver local oscillator it was impossible to attain long integration times toward sources of interest. ... I stepped in to investigate the problem. Tests I performed indicated that the fault was with the circuitry situated at the prime focus cabin of the 64m Parkes Radiotelescope. With the aid of a multimeter and portable cathode ray oscilloscope I proceeded exploring the circuitry associated with the subsystem. Without any familiarity of the subsystem, it took me some time to locate the fault, a shorted resistor. After I replaced it, the subsystem worked and we were able to detect the 2-2 transition of thioformaldehyde during the remaining one and a half days."

A partial, tentative identification of thioformaldehyde was also reported in comet Hale-Bopp by Woodney et al.


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