  The detection E-cyanomethanimine (E-HNCHCN) towards Sagittarius B2(N) is made
by comparing the publicly available Green Bank Telescope (GBT) PRIMOS survey
spectra (Hollis et al.) to laboratory rotational spectra from a reaction
product screening experiment. The experiment uses broadband molecular
rotational spectroscopy to monitor the reaction products produced in an
electric discharge source using a gas mixture of NH3 and CH3CN. Several
transition frequency coincidences between the reaction product screening
spectra and previously unassigned interstellar rotational transitions in the
PRIMOS survey have been assigned to E cyanomethanimine. A total of 8 molecular
rotational transitions of this molecule between 9 and 50 GHz are observed with
the GBT. E-cyanomethanimine, often called the HCN dimer, is an important
molecule in prebiotic chemistry because it is a chemical intermediate in
proposed synthetic routes of adenine, one of the two purine nucleobases found
in DNA and RNA. New analyses of the rotational spectra of both
E-cyanomethanimine and Z-cyanomethanimine that incorporate previous mm-wave
measurements are also reported.
