EQUILIBRIUM STRUCTURE AND HARMONIC FORCE-FIELD OF THE KNOWN PH3 AND THE UNKNOWN PH5

The equilibrium geometries and harmonic force fields of PH3 and PH5 are calculated in an ab initio way including electron correlation. The results for PH3 are in very good agreement with experimental values, whereas those for PH5 have to be regarded as predictions. We find for PH5 in its equilibrium D3 h structure rax = 1.47 Å, req = 1.42 Å and the harmonic vibration frequencies in Table 7 given under the heading CEPA". The barrier for Berry inversion is 2 kcal/mol. The ab initio calculation of phosphoranes such as PH5 not only requires the inclusion of polarization functions (d on P and p on H) but is also very sensitive to the choice of these polarization functions. This problem is taken care of by a detailed comparison of various basis sets. It is confirmed that a (10/6) basis for P in "double zeta contraction" is better balanced than a (12/9) basis in "double zeta contraction" and that the total energy is not a good criterion for the quality of a basis. © 1979 Springer-Verlag."