Knowledge Bank

The microwave spectrum of chloromethylphosphonic difluoride, $CICH2POF2$, has been investigated in the region from 26.5 to 30 GHz. The a-type R-branch transitions have been assigned for both the $\mathrm{<mrow\; data-mjx-texclass="ORD">35</mrow>}Cl$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">37</mrow>}Cl$ isotopic species for the trans conformer on the basis of the rigid rotor model. For the ground vibrational state the rotational constants for the $\mathrm{<mrow\; data-mjx-texclass="ORD">35</mrow>}CL$ isotope were found to be $A=4392.4\pm 2.3,B=1543.36\pm 0.01$ and $C=1512.30\pm 0.01$ MHz and for the $\mathrm{<mrow\; data-mjx-texclass="ORD">37</mrow>}Cl$ isotope: $A=4395.3\pm 2.7,B=1502.04\pm 0.01$ and $C=1472.54\pm 0.01$ MHz. With reasonably assumed structural parameters for the C-H and P=O distances as well as the HCH angle, a diagnostic least-squares adjustment was utilized to obtain the other six structural parameters. The infrared and Raman spectra have been recorded, and both the trans and gauche conformers have been identified in the vibrational spectra of the fluid phases. From a temperature study of the Raman spectrum of the liquid phase the enthalpy between the trans and gauche conformers was determined to be $370\pm 50cm-1$ (1.06 kcal/mol) with the trans conformer being thermodynamically preferred. Band contour simulation of the infrared gas phase bands also shows that the trans conformer is more stable in this phase. Upon crystallization only the trans conformer remains in the solid state. The asymmetric torsion for the trans conformer was observed as a series of closely spaced Q branches beginning at $82.5cm-1$ and falling to lower frequency and the corresponding transitions for the gauche conformer begin at $72.9cm-1$. These transitions have been used to obtain the potential constants for the asymmetric rotation.