High resolution FTIR spectra and analysis of the ν11 fundamental and of the ν2 + ν11, ν5 + ν12 and ν7 + ν16 combination bands of 12C6D6

Abstract

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 ν11 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 ν2 + ν11 (at 2798.1 cm−1), ν5 + ν12 (1802.5 cm−1) and ν7, + ν16 (2619.3 cm−1) of C6D6 has been analysed as well, from which improved values of the band origin and of the B and D j 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 (ν11 + ν16) − ν16 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 ν5, ν12 and ν16 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.