AN INFRARED STUDY OF THE SOLVENT EFFECT ON FREQUENCIES AND INTENSITIES OF CD AND CH STRETCHING BANDS OF d-CHLOROFORM, CHLOROFORM AND BROMOFORM

Abstract

The $CDCl_{3}$, $CHCl_{3}$ and $CHBr_{3}$ molecules have been studied in the gaseous state and dissolved in some slightly polar or non polar solvents. A Czerny-type spectrometer with a resolving power, $\frac{\nu}{\Delta\nu}$ = 75000 at 1.7 $\mu$ was used for the investigation of the first overtone band $2\nu_{1}$ of GASEOUS $CHCl_{3}$ and $CHBr_{3}$ molecules. The fundamental band $\nu_{1}$ at 3.3 $\mu$ of these molecules was recorded with a PFUND-type spectrometer (resolving power 10,000). The band-center $\nu^{gas}_{v^{\prime}^{\prime}\rightarrow v^{\prime}}$, the integrated intensity $A^{gas}_{v^{\prime}^{\prime}\rightarrow v^{\prime}}$ and some molecular constants were determined. The same parameters of the $\nu_{1}$, $2\nu_{1}$ and $3\nu_{1}$ bands of $CDCl_{3}$ were obtained by means of the PFUND-apparatus running in the first, second and third orders. The PFUND spectrometer is systematically used for the study of the LIQUID state. The half-width $\delta_{\nu}$ of the slit-function is small with respect to the width ($2\gamma$) of the infrared bands $\left(\frac{\delta_{\nu}}{2\gamma}=\frac{1}{20}\right)$ Thus the spectrometer recorded the true band profile. The values of $\nu^{solution}$ and $A^{solution}$ have been measured for the $\nu_{1}$ and $2\nu_{1}$ bands of $CHCl_{3}$ and $CHBr_{3}$ in the solvents: $CCl_{4}$, $C_{2}$ $Cl_{3}$, $CS_{2}$ and $CCl_{3}Br$. The same quantities were determined for the $v_{1}$, $2v_{1}$ and $3v_{1}$ bands of $CDCl_{3}$ in the solvents: $CCl_{4}$, $C_{2}$ $Cl_{4}$ and $CCl_{3}Br$. The observed harmonic vapor-liquid shifts were compared with the theoretical values (BUCKINGHAM). The solute-solvant interaction energy U arises from induction and dispersion forces. From the experimental value of $A^{gas}_{v^{\prime}^{\prime}\rightarrow v^{\prime}}$, were deduced the first coeffcients of the dipole moment function (HERMAN \& SHULER), i.e. $\left(\frac{\partial^{i}\mu}{\partial _{a}j}\right)_{o}$. These coefficients were necessary for the estimation of the induction energy. The experimental values of $A^{solution}_{v\rightarrow v^{\prime}}$ yielded the corresponding coefficients $\left(\frac{\partial^{i}M}{\partial _{q}i}\right)_{e}$ for the dissolved molecule. BUCKINGHAM’s relation between the coefficients $\left(\frac{\partial\mu}{\partial q}\right)_{o}$ and $\left(\frac{\partial M}{\partial_{q}}\right)_{e}$ was tested. The experimental rotational dipole correlation function, given by the following expression: $\Phi(t)=\int I(\omega)\cdot e^{i(\omega-\omega_{o})t}\cdot d\omega$, was calculated for the $\nu_{1}$ band of $CHCl_{3}$ and $CHBr_{3}$ molecules in the band gaseous state and dissolved in the solvents $CCl_{4}$ and $CS_{2}$. A comparison of these $\Phi_{n}$(t) functions showed that the hindrance to molecular rotation is greater in $CS_{2}$ that in $CCl_{4}$.