Interaction of NO ((NO)-N-15) with amorphous layers of Ru(II) carbonyl porphyrin (Ru(TPP)(CO), TPP2- = meso-tetraphenylporphyrinato dianion) was monitored by FTIR spectroscopy from 80 K to room temperature. An intermediate spectrally characterized at very low temperatures (110 K) with nu(CO) at 2001 cm(-1) and nu(NO) at 1810 cm(-1) (1777 cm(-1) for (NO)-N-15 isotopomer) was readily assigned to the mixed carbonyl-nitrosyl complex Ru(TPP)(CO)(NO), which is the logical precursor to CO labilization. Remarkably, Ru(TPP)-mediated disproportionation of NO is seen even at 110 K, an indication of how facile this reaction is. By varying the quantity of supplied NO, it was also demonstrated that the key intermediate responsible for NO disproportionation is the dinitrosyl complex Ru(TPP)(NO)(2), supporting the conclusion previously made from solution experiments.