Fig. 1: The mid-IR spectra of particles that contain nitrogen-rich organics.

The bottom two spectra are from particles that contained associated phyllosilicates and carbonates. The top spectrum contains very little phyllosilicate. The spectral bands are as follows: structural –OH at 3,685 cm⁻¹ (a), N–H stretch at 3,285 cm⁻¹ (b), a weak aromatic C–H stretch near 3,065 cm⁻¹ (c), aliphatic C–H stretch is a set of bands in the 3,000–2,820 cm⁻¹ range (d), a weak C≡N peak is visible at 2,145 cm⁻¹ (e), amide C=O stretch at 1,650 cm⁻¹ (f), N–H bend at 1,540 cm⁻¹ (g), CH₂ bend and C–O stretch in carbonates at 1,465 cm⁻¹ (h), C–N stretch at 1,410 cm⁻¹ (i), C–O stretch in aromatic ethers and CH₃ bending in the 1,255–1,240 cm⁻¹ range (j), Si–O stretch in phyllosilicates at 1,015 cm⁻¹ (k). Peak positions and assignments are summarized in Table 2. Insets: SEM images of Particles 2 and 33. Particle 26 was not analysed by SEM.