Conformational kinetics of methyl nitrite. I. NMR spectral evidence for statistical intramolecular vibrational redistribution

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Abstract
Pressure dependent rate constants for syn⇄anti conformational exchange in gaseous methyl nitrite and in gaseous methyl nitrite–CO2 mixtures have been obtained from line shape analyses of 1H NMR spectra. The pressure dependence of the exchange rates is consistent with a specific reaction rate constant of ∼1×109/s which agrees with RRKM calculations demonstrating that intramolecular vibrational redistribution is occurring at the statistical limit in methyl nitrite molecules with ∼12 kcal/mol of internal vibrational energy. At 12 kcal/mol methyl nitrite has a state density of ∼160/cm−1. These results indicate strong anharmonic and/or Coriolis coupling between vibrational levels. Bimolecular rate data for methyl nitrite and methyl nitrite–CO2 mixtures are consistent with a collisional efficiency βp for CO2 of 0.95(8) for activation of syn–anti conformational exchange at 258.8 K.