Knowledge Bank

Recently the Fermi resonance between $\nu 5$ and $\nu 3+\nu 6$ in $CH3I$ and between $\nu 4$ and $3\nu 6$ in $CH3Cl$ have been accurately analyzed in the gas phase. We have now studied those same resonances in spectra of $CH3I$ in solid matrices of $Ar,Kr,CO,N2$, and $CD3I$ and in spectra of $CH3Cl$ in solid matrices of $Ar,Kr,CO,N2$, and Xe. The observed frequencies and relative intensities are consistent with the gas phase spectra. It is found that the degree of resonance may be either diminished or enhanced in a manner which is readily explained by the frequency shifts in the solvent. In all cases, however, the interaction constant is not measurably changed from the gas phase constant. These results contradict the theoretical treatment given by $Strizhevsky1$ in which it is erroneously shown that the degree of Fermi resonance must always be enhanced in going from the gas phase to a condensed phase (either for pure substances or for solutions). Errors in Strizhevsky's work will be indicated and `a more nearly correct' theory of Fermi resonance in condensed solutions will be derived.