2013ApJ...767...66H

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 CH₂ NH and 170 lines of CH₃NH₂have been observed as individual, distinguishable features, although some are partially blended with other lines. For CH₂NH, the line profiles indicate V_LSR= 64.2±1.4 km/s and ΔV_1/2= 13.8±2.8 km/s, while V_LSR= 63.7±1.6 km/s and ΔV_1/2= 15.1±3.0 km/s 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 T_rot= 44 ±13 K and a column density of N_tot= (9.1±4.4)x10¹⁴/cm2 were determined from the analysis. For CH₃NH₂, T_rot= 159±30 K and N _tot= (5.0±0.9)x10¹⁵/cm2, indicating that this species is present in much warmer gas than CH₂NH. The fractional abundances for CH₂ NH and CH₃NH₂ were established to be f (H₂) ~ 3.0x10^–10 and f (H₂) ~ 1.7x10^–9, respectively. It has been proposed that CH₂ NH 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 CH₂ NH and CH₃NH₂in Sgr B2, it is improbable that these species are closely related synthetically, at least in this source. Both CH₂ NH and CH₃NH₂are more likely created by neutral-neutral processes in the gas phase.