Infrared diode-laser spectrum of the CH 3CN ν2 band . Analysis of local resonances with ν6±1 + 2 ν8±2, ν4 + ν7±1 + ν8±1, ν4 + ν6±1, ν4 + ν7±1, and 2 ν70 + ν8±1 states
Fifty-one sections of infrared diode-laser spectra of acetonitrile have been measured in the region from 2283.5 to 2235.7 cm -1. About 450 transitions belonging to the ν2 band have been assigned for K ≦ 7 and J ≦ 44. Anomalies found in the rotational structure have been proven to be due to five local resonances. Observed transition frequencies have been fitted by a least-squares method to a model which includes Fermi-type resonances (∆ k = 0, ∆ℓ = ± 3 n) with ν6±1 + 2 ν8±2 and ν4 + ν7±1 + ν8±1 states, x, y-type Coriolis resonances (∆ k = ±1, ∆ℓ = ∓3 n ± 1) with ν4 + ν6±1 and ν4 + ν7±1 + ν8±1 states, and a centrifugal-distortion-type resonance (∆ k = ±2, ∆ℓ = ∓3 n ± 2) with a 2 ν70 + ν8±1 state. The 11 × 11 dimensional energy matrix has been diagonalized in order to obtain the perturbed energy levels. The standard deviation for the fit is 1.075 × 10 -3 cm -1. The molecular constants determined are also listed.