INSIGHTS INTO SURFACE HYDROGENATION IN THE INTERSTELLAR MEDIUM: OBSERVATIONS OF METHANIMINE AND METHYL AMINE IN Sgr B2(N)

Multiple observations of methanimine (CH2NH) and methyl amine (CH3NH2) have been performed toward Sgr B2(N) at 1, 2, and 3 mm using the Submillimeter Telescope and the 12 m antenna of the Arizona Radio Observatory. In the frequency range 68–280 GHz, 23 transitions of CH2NH and 170 lines of CH3NH2 have been observed as individual, distinguishable features, although some are partially blended with other lines. For CH2NH, the line profiles indicate VLSR = 64.2 ± 1.4 km s−1 and ΔV1/2 = 13.8 ± 2.8 km s−1, while VLSR = 63.7 ± 1.6 km s−1 and ΔV1/2 = 15.1 ± 3.0 km s−1 for CH3NH2, parameters that are very similar to those of other organic species in Sgr B2(N). From these data, rotational diagrams were constructed for both species. In the case of CH2NH, a rotational temperature of Trot = 44 ± 13 K and a column density of Ntot = (9.1 ± 4.4) × 1014 cm−2 were determined from the analysis. For CH3NH2, Trot = 159 ± 30 K and Ntot = (5.0 ± 0.9) × 1015 cm−2, indicating that this species is present in much warmer gas than CH2NH. The fractional abundances for CH2NH and CH3NH2 were established to be f (H2) ≈ 3.0 × 10−10 and f (H2) ≈ 1.7 × 10−9, respectively. It has been proposed that CH2NH is formed on grains via hydrogenation of HCN; further hydrogenation of CH2NH on surfaces leads to CH3NH2. However, given the dissimilarity between the rotational temperatures and distributions of CH2NH and CH3NH2 in Sgr B2, it is improbable that these species are closely related synthetically, at least in this source. Both CH2NH and CH3NH2 are more likely created by neutral–neutral processes in the gas phase.