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Transactions of the Faraday Society


Transactions of the Faraday Society was published from 1905 - 1971.

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Paper

Trans. Faraday Soc. , 1971, 67, 257 - 271, DOI: 10.1039/TF9716700257

Kinetics and mechanism of the vibrational relaxation of NOX2(v= 1) in the temperature range 100–433 K

J. Billingsley and A. B. Callear

The first vibrational level of NOX2 was excited with an intense light flash and relaxation times were measured from 100 to 433 K. At 210 K and below, the rate equation is –d[NO(= 1)]/dt=[NO(= 1)](k1[NO]+k2[NO][M]). k1 is the rate coefficient for self-relaxation in bimolecular collisions and varies inversely with temperature. The term k2[NO][M] corresponds to vibrational relaxation in ternary collisions.The negative temperature coefficient for relaxation in bimolecular collisions was interpreted qualitatively by postulating that the potential energy of the resonance for an electronic-vibrational transition is orientation dependent; the lowest resonance potential may correspond to the most stable configuration of the (NO)2 dimer. The role of ternary collisions is probably to remove NOX2(= 1) as stabilized dimer. From the dissociation constants of the dimer, rates of bimolecular dissociation were computed assuming that k2 corresponds to the rate coefficient for dimerization. The magnitudes of the bimolecular rate coefficients were consistent with the energy transfer model, provided all degrees of freedom can contribute efficiently to bond rupture. Rate coefficients for vibrational exchange from NO to N2 were measured at 298 and 433 K. Evidence for vibrational equilibrium was found in experiments with NO + CO mixtures at low temperature.