A novel method is proposed for studying the thermal decay of the oxygen-coordinated nitrosyl metastable states. Having examined 18 different ruthenium nitrosyl complexes, we observed that, upon photoinduced rotation from Ru-NO to Ru-ON coordination, the frequency of the nitrosyl valence bands shifts, on average, by 126 +/- 15 cm(-1). The thermal stability of the product Ru-ON state is qualitatively characterized (decay temperature, Arrhenius activation energy, and pre-exponential factor) using infrared absorption of the NO group, in comparison with the reference complex(es), which are all heated in the same KBr disk during temperature sweep.