Knowledge Bank

Three perpendicular bands of $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C6H6$ and two bands of $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}C5D5$ have been measured with high resolution Fourier transform instruments to provide reliable data necessary for calculations of the force field for the benzene molecule. Analysis of the $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C6H6$, bands $\nu 14,\nu 13$ and $\nu 12$ near 1018 , 1454 and 3065 $cm-1$ respectively, and of the $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}C6D6$ bands 14 and and $\nu 13$ near 814 and $1335cm-1$, yielded accurate values for the band origins , Coriolis coupling parameters , for the vibrational dependences of the rotational constants B and C, as well as for the ground state constants $Bq,D0J$, and $DJK0$ of these molecules. It is found that the observed isotopic shifts in the values of the Coriolis constants $\xi t$ on substitutions $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}C5\to 13C6$ and $H6\to D6$ cannot be accurately accounted for by a general harmonic force field for the $E14$ normal modes of benzene, probably due to anharmonic effects.