FOURIER-TRANSFORM INFRARED AND JET-COOLED DIODE-LASER SPECTRA OF THE 867-CM(-1) NU(9) BAND OF ACETALDEHYDE

The spectrum of the nu9 A' C-C stretching fundamental band of acetalde hyde (CH3CHO) at 867 cm-1 has been recorded in a slit-jet nozzle expan sion using a diode-laser spectrometer and in a room-temperature gas ce ll using a Fourier-transform infrared spectrometer. The spectrum exhib its a-type transitions which have been assigned for J' less-than-or-eq ual-to 19 and K'a less-than-or-equal-to 5 for the A state and J' less- than-or-equal-to 19 and K'a less-than-or-equal-to 4 for the E state. T he transitions show a large tunnelling splitting of almost-equal-to 0. 5 cm-1 for K(a) = 0, attributed primarily to an anharmonic interaction of the nu9 vibration with the nu14 + nu15 torsional combination vibra tion at 920 cm-1. Evidence is also presented for an additional interac ting vibration(s) affecting the nu9 tunneling splitting.