THE NO DIMER : 15N ISOTOPIC INFRARED SPECTRA, LINE-WIDTHS, AND FORCE FIELD

The v 1 fundamental bands of (15N16O)2 and 14N16O-15N16O isotopes of the NO dimer have been studied using a long-path (200 m) low temperature (84 K) gas cell and Fourier transform infrared spectrometer. The spectra, obtained with a resolution of 0·005 cm-1, were analysed to give accurate rotational and quartic centrifugal distortion parameters for the ground and the v 1 = 1 vibrational states. The predissociation-limited v 1 band line width for (14N16O)2 was measured to be 0·0056(3) cm-1, which is slightly less than previous determinations. The (15N16O)2 width was found to be 0·0044(2) cm-1, and the significant isotope dependence will help to constrain models of the predissociation process. A much larger width of 0·014(2) cm-1 was measured for the mixed isotope, 14N16O-15N16O. This, and the mixed isotope vibrational frequency, may be understood on the basis of a simple coupled-oscillator model. The present results were used to derive a refined structure for the NO dimer: r(NO) = 1·1515(3) A, r(NN) = 2·263...

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