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The first direct kinetic measurements have been made on the reaction NO + NO2⇌ N2O3. Equilibrium mixtures of the nitrogen oxides containing excess NO at 208 ± 3 K were perturbed by flash photolysis of a fraction of the N2O3. The rate of relaxation to equilibrium was monitored by observing the transmittance of a line from a cw CO laser selected to coincide with the vband in N2O3. At pressures up to 1000 Torr (M = He, Ar) the association reaction is third-order with k0(M = He) = (3.6 ± 0.15) × 10−33cm6molecule−2s−1and k0(M = Ar) = (5.5 ± 0.8) × 10−33cm6molecule−2s−1.

The spectrum of the symmetric top, hydrogen-bonded heterodimer H3N-HCN has been recorded between 2900 and 3200cm-1 using a high resolution FTIR spectrometer. The more intense bands are associated with the ν2 (H-CN stretch) vibration and include hot bands associated with the low frequency modes ν5, ν2 and ν10. Weaker difference bands of the type ν2+(n-1) ν5-nν5 are also observed. Analysis of the bands yields values for the band origins: ν2/0=3110·5±0·2cm-1 and ν5/0=140±5cm-1 and the anharmonicity constants: x2,10=12·7±0·5cm-1, x2,9≈x2,5=23±3cm-1 and x5,10=-5±2cm-1. The lifetime in ν2 with respect to vibrational predissociation, estimated from the width of the sharpest observed feature, is 100-200 ps but there is some indication that this lifetime may decrease at high J.

The fundamental and first three overtone bands associated with the v1 (NO stretching) vibration of the planar, asymmetric top molecule N2O3 have been studied at ca 230K under high spectral resolution using a Fourier transform infrared spectrometer. Even for the v1 band, where the spectrum is obtained at 0·005 cm-1 resolution, the complexity of the rotational structure defies complete analysis. However, from (i) the sharp P and R branch features associated with coincidences between transitions with high J and low K, (ii) simulations of the shape of the main type A Q branch, and (iii) the relationship between the three moments of intertia of a planar molecule, it has been possible to deduce the wavenumbers of the band origins (v01 = 1829·535(2), 2v01 = 3628·03(5), 3v01 = 5394·124(10) and 4v01 = 7128·5 ± 1 cm-1) and, for v1, 2v1 and 3v1, the rotational constants, A', B' and C'.Hot bands make a considerable contribution to the spectrum in the region of each main band. A number of type A Q branches have been assigned and, from the frequency shifts from the origin of the main bands, the anharmonicity constants x16, x17 and x19 have been estimated.The upper states of the overtone bands all lie above the dissociation limit for N2O3 → NO + NO2. The linewidths observed for some transitions in the 2v1 and 3v1 bands indicate lifetimes of (180-300) ps and > 150 ps, respectively, demonstrating that intramolecular energy flow from the v1 mode is relatively slow and that, in this respect, N2O3 exhibits 'non-RRKM behaviour'.