Analysis of the ν9ν10 band system of allene

The infrared spectrum of allene has been recorded with high resolution (0.002-0.004 cm^?1) on a Fourier transform instrument in the region 730 to 1170 cm^?1 containing the perpendicular bands, ν₉ and ν₁₀. A total of 21 subbands with KΔK ranging from ?6 to +14 have been assigned in the ν₉ band, and 26 subbands with KΔK = ?10 to +15 have been assigned in the ν₁₀ band. The bands are affected by a combination of a J_z-Coriolis and a quartic anharmonic interaction between their upper states ν₉ and ν₁₀. In addition, several other more localized perturbations are found in the spectrum. The nature of the interactions responsible for these perturbations is discussed, and five of the strongest perturbations are quantitatively accounted for by constructing a Hamiltonian matrix which includes five different perturbing states and their Coriolis and anharmonic resonances with the ν₉ and ν₁₀ upper states. A set of spectroscopic constants for the ν₉ and ν₁₀ states and for some of the perturbing states is reported.