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Description
Methylamine (CH_3_NH_2_) is a light molecule of astrophysical interest, which has an intensive rotational spectrum that extends in the submillimeter wave range and far beyond, even at temperatures characteristic for the interstellar medium. It is likely for ^13^C isotopologue of methylamine to be identified in astronomical surveys, but there is no information available for the ^13^CH_3_NH_2_ millimeter and submillimeter wave spectra. In this context, to provide reliable predictions of ^13^CH_3_NH_2_ spectrum in millimeter and submillimeter wave ranges, we have studied rotational spectra of the 13C methylamine isotopologue in the frequency range from 48 to 945GHz. The spectrum of ^13^C methylamine was recorded using conventional absorption spectrometers in Lille and Kharkov. The analysis of the rotational spectrum of ^13^C methylamine in the ground vibrational state was performed on the basis of the group- theoretical high-barrier tunneling Hamiltonian that was developed for methylamine by Ohashi and Hougen. The available multiple observations of the parent methylamine species toward Sgr B2(N) at 1, 2, and 3mm using the Submillimeter Telescope and the 12 m antenna of the Arizona Radio Observatory were used to make a search for interstellar ^13^CH_3_NH_2_. In the recorded spectra, we have assigned 2721 rotational transitions that belong to the ground vibrational state of the ^13^CH_3_NH_2_. These measurements were fitted to the Hamiltonian model that uses 75 parameters to achieve an overall weighted rms deviation of 0.73. On the basis of these spectroscopic results, predictions of transition frequencies in the frequency range up to 950GHz with J<50 and Ka<20 are presented. The search for interstellar ^13^C methylamine in available observational data was not successful and therefore only an upper limit of 6.5x10^14^cm^-2^ can be derived for the column density of ^13^CH_3_NH_2_ toward Sgr B2(N), assuming the same source size, temperature, linewidth, and systemic velocity as for parent methylamine isotopic species.
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