Analysis of theν3,ν6,ν7+ν8Fermi and Coriolis interacting band system in methyl cyanide

A reinvestigation of the Fermi and Coriolis interacting band system ν 3, ν 6, ν 7 + ν 8 of methyl cyanide has been performed with a resolution better than 0·3 cm-1. The observed J structure in some of the K sub-bands enables an unambiguous numbering of the sub-band Q branches to be made. The resulting assignment, which differs from Amat and Nielsen's previous assignment, is used to re-analyse the band system. A band contour has been calculated by computer simulation, including the effects of both the Fermi resonance of ν 6 with ν 7 + ν 8 and the Coriolis resonance of ν 6 with ν 3; both the frequency and intensity perturbations which result have been accurately reproduced. The molecular parameters obtained from our analysis are summarized in table 2.