Knowledge Bank

In the high resolution infrared spectra of both the $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C2$ and the $d4$ isotopomers of 1,2-difluoroethane, a B-type band has been analyzed. This band, which is due largely to antisymmetric CF bending, is at $279.410cm-1$ for the $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C2$ species and at $264.257cm-1$ for the $d4$ species. From fitting 663 ground state combination differences (GSCD) to a Watson-type Hamiltonian, GS rotational constants for the $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C2$ species are $A=1.022398(2),B=0.128825(8)$, and $C=0.119682(8)$ $cm-1$ with $\kappa =0.9798$. From fitting 950 GSCDs, the GS rotational constants for the $d4$ species are $ A = 0.6902091 (11), B = 0.1253009 (6)$, and $C=0.1154862(6)$ $cm-1$ with $\kappa =-0.9658$. Upper state constants have also been fitted to the central parts of the bands. From the GS constants for the $d0$ $speciesa$ as well as for the $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C2$ and $d4$ species, a largely $r5$ structure has been found. These structural paramenters will be compared with those of the gauche rotamer found from microwave $spectroscopy.b$