The high-resolution infrared absorption spectrum of the oxalodinitrile di-N-oxide ͑ONCCNO͒ molecule has been recorded in the gas phase with a Fourier transform spectrometer at a resolution of 0.003 cm Ϫ1 . No previous high-resolution spectra have been recorded for this semistable palindromic molecule. On the basis of the 2:1 intensity alternation in the rotational lines caused by nitrogen nuclear spin statistics, the ONCCNO molecule appears to be linear. A quasilinear structure, however, cannot

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... be ruled out at this stage of the analysis. The 4 and 5 fundamental modes at 2246.040 55͑23͒ cm Ϫ1 and 1258.475 30͑11͒ cm Ϫ1 have been analyzed to give ground state rotational constants of B 0 ϭ0.042 202 10͑96͒ cm Ϫ1 and D 0 ϭ8.77͑70͒ϫ10 Ϫ10 cm Ϫ1 . By fixing the CN and NO bond lengths to 1.1923 and 1.1730 Å, respectively, the C-C bond length was determined to be 1.3329 Å using the B 0 value. This short C-C bond length is thus similar to that observed for a carbon-carbon double bond.