No abstract

All molecules having dipole moments greater than 1.625 D (0.639 ea0) have positive electron affinities in the Born–Oppenheimer approximation (i.e., when the nuclei are stationary). However, when nuclear motion is treated exactly, the above sufficient condition for binding an extra electron is modified. We have determined the magnitudes of Born–Oppenheimer electron affinities which are required in order to insure that the negative ions of polar molecules (μ≳1.625 D) are still stable when the nuclei are free to move.

The influence of a molecule's dipole moment on its ability to capture an electron into a stable bound state is examined. It is proved that, in the fixednuclei approximation, a value greater than 1"625 Debye for the dipole moment suffices to guarantee the existence of a discrete spectrum of negative ion states. Implications for Hartree-Fock calculations of negative ions are discussed. The interaction of electronic, vibrational and rotational motions in negative dipolar ions is studied, and conclusions are drawn for real molecules.

2) Uncertainties in the nuclear wave functions. More recent Cabibbo-model predictions 9 of P y cc (1.08 MeV) are in qualitative agreement with, and somewhat larger than, the results of Ref. 8.(3) The "enhancement factor" to be expected from the neutral weak currents is difficult to calculate precisely; current estimates 10 for the Weinberg-Salam model point to a value of about 10. The 18 F system is one of the most favorable cases, both experimentally and theoretically, for studying AT= 1 PNC forces. With the Cabibbomodel prediction of Ref. 8, the present experiment yields an upper limit of 7.5 for the "enhancement factor" produced by neutral weak currents. 11