The ν4 Vibration–Rotation Bands of C6H6 and C6D6: The Analysis of the Bands and the Determination of the Bond Lengths

Abstract
The ν4. vibration–rotation bands of benzene and benzene-d6 have been recorded with high resolution. The K = 0 subbands have been analyzed and spectroscopic constants for both vibrational states have been calculated. Assuming D6h symmetry for the molecules the bond lengths have been determined from the ground state rotational constants of the two isotopic molecules. The values obtained are: r0(C—C) = 139.64 ± 0.02 pm and r0(C—H) = 108.31 ± 0.13 pm.