We are studying H13C14N spectra by saturated absorption spectroscopy, where HCN pressures of several units of Pascals are used. The gas is filled in a fused silica/quartz cell which inner surface is passivated to suppress a setting of HCN on the cell walls due to HCN's dipole moment. But still, we observe a slow decay in our spectroscopic signal. Could anybody confirm or explain if HCN suffers from molecule decomposition (at pressures ~1-10 Pa) and if there is a way how to minimise it? Thanks a lot!