if you want to clarify decomposition products, then you need at least high-resolution mass spectrometry (e.g. TOF) to determine the exact mass of your decomposition products. However, this only helps you to a limited extent with the structural elucidation. For this you need at least 1H-NMR. Do you have the possibility to isolate the decomposition products on a preparative scale? 1 to 2mg should be sufficient for NMR analysis if you use a microprobe head.
Decomposition products can be observed only if your instrument has that much of resolution and they are stable in that time range. For example, assume your decomposed products have life times in ms time sclae, for good monitoring your detectors should have at least us time sclae.
Further, how are you going to do irradiation in the column inside?