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	Figure 1: Four six-membered cyclic aromatic molecules: 1. benzene; 2. pyridine; 3. pyrimidine; and 4. 1,3,5-triazine (or s-triazine), having zero, one, two, and three nitrogens per ring, respectively.
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In the text

Figure 2: The FT-IR spectra of pyridine, pyrimidine and s-triazine ( top to bottom) isolated in an argon matrix at 12 K in the ranges 3500-3000 cm-1 ( left panels) and 1800-600 cm-1 ( right panels) with a resolution of 1 cm-1. The matrix isolated molecules were irradiated with UV for 10 s, 1 and 10 min. The vertical scale bars indicate the infra-red absorption in absorption units. Band assignments are presented in Table 1. New bands appearing after photolysis are designated by asterisks (). Photoproduct assignments are given in Table 3. Features at 1383, 1344 and 1234 cm-1, designated with arrows, are due to contamination in the system. These contaminations were accumulated outside the argon matrix and did not interfere with the photolysis reactions.

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In the text

Figure 3: The half-lives of the three N-heterocycles plotted against the number of nitrogen atoms in the ring. Also included in this graph is the half-life of benzene, taken from Ruiterkamp et al. (2005). This plot shows that the photostability of small heterocyclic molecules decreases when an increasing number of nitrogen atoms is incorporated in the ring. The error bars indicate the standard deviation of the linear fit used in the calculation of the half-lives of those molecules.

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In the text

	Figure 4: The relative column densities of s-triazine and its photoproducts during photolysis. Shown in the graph are s-triazine (graph: , inset: a - measured by the 1552 cm-1 transition), c-(HCN)3 (graph:  , inset: b - from the 3264 cm-1 vibration) and CNCN (graph: , inset: c - from the peak at 2295 cm-1). Inset: the suggested photolysis reaction pathway for s-triazine upon irradiation with UV.
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In the text