Analysis of the 3μm bands of benzene
Abstract
A comprehensive rovibrational analysis is reported for the 3μm absorption bands of the benzene molecule measured on a differencefrequency laser spectrometer and deconvolved to an effective linewidth of 0.00100.0015 cm ^{1}. The four strong bands observed, centered at 3047.908, 3078.614, 3100.408, and 3101.854 cm ^{1}, are due to the E_{1 u} fundamental ν_{12} sharing its intensity with the E_{1 u} components of the combinations ν_{13} + ν_{16}, ν_{2} + ν_{13} + ν_{18}, and ν_{3} + ν_{10} + ν_{18} via anharmonic resonances. The bands exhibit strong perturbations due to l resonances with the inactive {B _{1u}}/{B _{2u}} components of the ν_{13} + ν_{16} and ν_{2} + ν_{13} + ν_{18} states, and numerous localized perturbations due to overtones and combinations of the 16 lowfrequency vibrations of the molecule. Symmetry arguments and values of constants such as Cζ known for the fundamentals have been used to propose tentative assignments for many of the perturbing states. The Hamiltonian matrix used for the treatment of the 8384 assigned transitions, with all the components of the main interacting states plus 18 perturbing states, was of order 34 and contained 130 parameters of which 112 were eventually adjusted. A set of spectroscopic constants is reported which reproduces all the data with a standard deviation of 0.0012 cm ^{1}. The analysis shows that the Fermi resonance between ν_{12} and ν_{13} + ν_{16} combined with the other anharmonic interactions shifts the fundamental down by 16.46 cm ^{1} from its unperturbed position. It is found that x,yCoriolis and anharmonic resonances of surprisingly high order have to be invoked to account for most of the localized perturbations observed in the spectrum.
 Publication:

Journal of Molecular Spectroscopy
 Pub Date:
 November 1987
 DOI:
 10.1016/00222852(87)900798
 Bibcode:
 1987JMoSp.126...82P