THE INFRARED-SPECTRUM OF METHYL CYANIDE BETWEEN 1240 AND 1650 CM(-1) - THE COUPLED BAND SYSTEM NU(3), NU(6)(+ -1), AND NU(7)+NU(8)(+/-2)/

A Fourier transform spectrum with a resolution of 0.002 cm-1 of CH3CN has been studied in the spectral region of 1240-1650 cm-1. The region covers the bands nu3, nu6(+/-1), and nu7 + nu8 which are coupled by ve ry strong Fermi and Coriolis interactions. More than 3900 lines were a ssigned in the spectrum, mostly to the bands nu6(+/-1) and nu7 + nu8(/-2). The rotational structure of these bands including the Q branches was almost completely resolved. The PAPE component of nu7 + nu8 WaS n ot detected. For the weak nu3 band, which has not been observed earlie r directly, we were able to assign the two subbands K = 5 and 6 around the nu3/nu6 Coriolis resonance crossing region. A least-squares fit w ith 42 parameters and about 20 interactions led to a standard deviatio n of 0.0072 CM-1. (C) 1994 Academic Press, Inc.