THE $\upsilon_{13}$ FUNDAMENTAL BAND OF BENZENE

Abstract

The perpendicular band of the $E_{1u}$ vibration $\upsilon_{13}$ of benzene, occurring near $6.7 {\mu} m$, has been measured on a BOMEM high-resolution Fourier transform spectrometer with a 246 cm optical path difference. The observed line width (full width at half height) of $-0.0048 cm^{-1}$ was reduced by deconvolution to $-0.0020 cm^{-1}$, which is slightly below the Doppler limit. The dense rotational structure was well resolved, and it was possible to assign over 120 subbands in the region $1466-1504 cm^{-1}$. A perturbation, identified as a third-order $J_{x, y}$-Coriolis interaction with a state (presumably the $A_{2u}$ component of $\upsilon_{4}+2\upsilon_{20}$) located only $-0.055 cm^{-1}$ above the fundamental, causes distortion of the rotational structure and formation of subband heads in the low-k $P_{Q}$-branches, which exhibit a striking line-like shape, The spectrum was analyzed in detail with the aid of the computer program SYMTOP for the treatment of symmetric top bands whose upper states are involved in arbitrary interactions. Some of the spectroscopic constants obtained for the $\upsilon_{13}$ state are $\upsilon_{o}=1483.9852 cm^{-1}; \alpha^{u}=B'-B_{0} =-6.36\times 10^{-5} cm^{-1}; \alpha^{C} = C'-C_{0} =-9.40\times 10^{-5} cm^{-1}; C\zeta = -2.671\times 10^{-2} cm^{-1} q=-2.95\times 10^{-4} cm^{-1}$, the over-all standard deviation of the fit was $0.0005 cm^{-1}$.