Knowledge Bank

“Because of some inconsistencies in the previous $work,1$ we have redetermined the anharmonicity constants $x1$ for the $CY3X$ molecules (Y=H or D; X=F, CI, Br, or I), using the equations of Hansen and $Dennison.2$ For the $a1$ and e C-H stretching, and the e H-C-H bending, vibrations, the $x1\prime s$ reported by $Dennison2$ for $CH4$ were used. For the $a1C-X$ (diatomic-molecule-like) stretching vibration, several values of $xa$ were selected in a range determined by the $xa$ values of diatomic molecules containing similar atoms, and values of $x2$ were calculated for each of these. The $\omega i$ values were then obtained from the observed wave numbers $\sigma i$ and the relation $\sigma i=\omega i(1-xj)$. The six $xi\prime s$ corresponding to those $\omega i\prime s$ which best satisfied the Teller-Redlich product rule were then taken as the best values. The $xi\prime s$ thus obtained for $\sigma 1(a1),\sigma 2(a1),\sigma 3(a1),\sigma 4(e),\sigma 5(e),$ and $\sigma 6(e)$ wee respectively: [FIGURE] In the product rule, $\Pi i\omega i(CH3X)/\Pi i\omega i(CD3X)=|GCH2X|1/2|GCD2X|1/2|GCD1X|1/2$ to 5 significant figures for the $a1$, and 4 for e, species. The present $xi\prime s$ seem more consistent and meaningful than the previous values.”