High-resolution spectrum of the nu 9 band and reinvestigation of the nu 8 band of cis-CH3ONO

The infrared spectrum of methyl nitrite CH3ONO has been recorded at a spectral resolution of 0.003 cma1 using a Fourier-transform spectrometer Bruker IFS125HR. The nu 8 band of the cis isomer has been reinvestigated in the 780-880 cm-1 spectral range to complete the study made by Goss et al. (2004) [3] and to fit the internal rotor splittings. The BELGI-IR program, which enables us to treat an isolated infrared band for asymmetric molecules containing one internal methyl rotor has been used for the analysis and predictions of spectra. Finally 1036 lines (913 A-type and 123 E-type lines for J less than or equal to 50 and Ka less than or equal to 28) have been assigned for the cis isomer and fitted with a standard deviation of 0.00047 cm-1. Furthermore, for the first time, the nu 9 band of cis-CH3ONO was investigated in the 540-660 cm-1 spectral range and rather large internal rotation splittings were also observed at higher J values. For the nu 9 band, the effective approach performed with the BELGI-IR program allowed us to analyze and reproduce 682 lines up to J=50 and Ka=18 with a standard deviation of 0.00051 cm-1. The multiple vibrationarotationatorsion interactions, which are likely to occur between the excited v9=1 and v8=1 states and the torsional manifolds are discussed.