Knowledge Bank

The Raman spectra (3500 to $30cm-1$) of gaseous and solid methoxydichlorophosphine. $CH3OPCI2$, have been recorded and only the trans conformer (methyl group trans to the phosphorus lone pair) is present in either spectrum. Additionally, the far infrared spectrum of the gas has been recorded from 350 to $30cm-1$ at a resolution of $0.10cm-1$. The fundamental asymmetric torsional and methyl torsional modes are extensively mixed and have been observed at 120 and $58cm-1$, respectively. Estimates are given for the potential functions governing these anharmonic modes. A complete vibrational assignment is given for both the normal and $d3$-isotopomer. The fundamental vibrational frequencies and barriers to internal rotation which have been obtained experimentally are compared to those obtained from ab initio Hartree-Fock calculations employing the $3-21G\ast$ basis set. The structural parameters and relative conformer stabilities have been obtained with the $RHF/6-31G\ast$ basis set as well as with electron correlation at the MP2 level. From these calculations, the gauche conformer is estimated to be more than 4.0 kcal/mol less stable than the trans conformer which is consistent with the observation of only the trans conformer in the Raman spectrum of the gas at ambient temperature. All of these results are discussed and compared with the corresponding quantities obtained for some similar molecules.