Rotationally resolved spectroscopy of the ν8 band of cis-methyl nitrite

The 770-880 cm⁻¹ region of the methyl nitrite spectrum has been recorded at a resolution of 0.0015 cm⁻¹ in a static cell. Consistent with published determinations of the barrier to internal rotation of the methyl group, bands belonging to the trans isomer are very congested while those belonging to the cis isomer are more tractable. A total of 634 lines have been assigned in the ν₈ vibrational band of the cis isomer. These lines and 32 microwave lines have been globally fit to a Watson-type Hamiltonian with an rms deviation of 0.00044 cm⁻¹. An additional 150 lines were also assigned but were not included in the fit because they were split by 0.001-0.005 cm⁻¹, much larger than previously reported torsional or hyperfine splittings.