High resolution FTIR spectra and analysis of the nu(11) fundamental and of the nu(2)+nu(11), nu(5)+nu(12) and nu(7)+nu(16) combination bands of (C6D6)-C-12

We report results from measurements of the high resolution FTIR spectrum for the fully deuterated benzene molecule C6D6 in the range 450-3500 cm(1). Accurate spectroscopic constants have been obtained for the fundamental vibration nu(11) at 496.208 cm(1) and improved ground state constants have been deduced from a fit of ground state combination differences. The J structure of the combination parallel bands nu(2) + nu(11) (at 2798.1 cm(1)), nu(5) + nu(12) (1802.5 cm(1)) and nu(7) + nu(16) (2619.3 cm(1)) of C6D6 has been analysed as well, from which improved values of the band origin and of the B and DJ constants of the excited states have been obtained. The strongest hot bands accompanying these parallel transitions have been assigned by means of the anharmonic force field calculated by MASLEN et al. [1992, J. chem. Phys., 97, 4233]. In particular (nu(11) + nu(16)) - nu(16) is assigned to the band at 492.4 cm(1) even though its shape is typical of a perpendicular transition (PAPE). New values for the nu(5), nu(12) and nu(16) band origins are determined from the band origins of combination bands and from calculated anharmonic constants. Numerous anharmonic constants are derived from the assignment of hot band and combination transitions.