Formation of peptide bonds in space: A comprehensive study of formamide and acetamide in Sgr B2(N)

Extensive observations of acetamide (CH₃CONH₂) and formamide (NH₂CHO) have been conducted toward Sgr B2(N) at 1, 2, and 3mm using the Submillimeter Telescope (SMT) and the 12m antenna of the Arizona Radio Observatory. Over the frequency range 65-280GHz, 132 transitions of acetamide have been observed as individual, distinguishable features, although in some cases they are partially blended. The unblended transitions in acetamide indicate V _LSR= 63.2 2.8kms^-1 and ΔV _1/2= 12.5 2.9kms^-1, line parameters that are very similar to that of formamide (NH₂CHO) and other organic species in Sgr B2(N). For formamide, 79 individual transitions were identified over the same frequency region. Rotational diagram analyses indicate the presence of two components for both species in Sgr B2(N). For acetamide, the colder component (E_u < 40K) exhibits a rotational temperature of T _rot= 17 4K and a column density of N _tot= 5.2 3.5× 10 ¹³cm^-2; the higher energy component has T _rot= 171 4K and N _tot= 6.4 4.7× 10¹⁴cm^-2. In the case of formamide, T _rot= 26 4K and N _tot= 1.6 0.7× 10¹⁴cm^-2 for the colder component with T _rot= 134 17K and N _tot= 4.0 ± 1.2× 10 ¹⁴cm^-2 for the warmer region. The fractional abundances of acetamide are f (H₂)= 1.7× 10^-11 and 2.1× 10^-10 for the cold and warm components, and in formamide, f (H ₂)= 5.3× 10^-11 and 1.3× 10^-10. The similarity between the abundances and distributions of CH₃CONH ₂ and NH₂CHO suggests a synthetic connection. The abundance of acetamide, moreover, is only a factor of three lower than that of formaldehyde, and very similar to acetaldehyde and ketene. CH ₃CONH₂ is therefore one of the most abundant complex organic species in Sgr B2(N), and could be a possible source of larger peptide molecules, as opposed to amino acids.