High-resolution FTIR spectroscopy using a jet:: Sampling the rovibrational spectrum of 12CH4

We have recorded high-resolution absorption spectra of (CH4)-C-12 cooled in a jet, using a Fourier transform interferometer. The expected nuclear spin symmetry conservation in the jet is exhibited from data recorded around 3000 cm(-1) showing the relative intensity of the lines starting from the J " = 2 para and ortho levels. Spectra recorded around 4300 cm(-1) are used to validate existing rovibrational parameters. Spectra recorded around 6000 cm(-1) allow new rovibrational assignments to be performed in the N = 4 polyad. In particular, lines in the upsilon(1) + upsilon(3) band are identified for the first time. (C) 1998 Academic Press.