Nuclear quadrupole interaction in solid HF and trifluoroaminoboranes

Abstract

Using the time differential perturbed angular distribution method (TDPAD) solid HF and trifluoroaminoboranes have been investigated. In the case of solid HF some new aspects appear in the interpretation of former experiments. The new measurements either reproduce the older data that yielded one frequency and a distinct ν, or show two frequencies and no distinct ν. This discrepancy can be explained with different target preparations. While the one-frequency experiments were done with untempered targets the two-frequency targets were tempered. Trifluoroaminoboranes (F 3BNH 3) are known as charge-transfer complexes. Since ammonia acts preferentially as an electron donor and 19F is the most electronegative element, a lowering of the observed coupling constant should appear. Experiment, however, does not support this; it gives an unchanged coupling constant, but the asymmetry parameter is changed by a factor of more than 2. This behaviour can be understood by calculating the electron distribution in both molecules within the framework of the Townes and Dailey theory. It turns out that charge transfer does take place, but the transferred charge does not lead to a more isotopicc electronic environment for fluorine, but rather reduces the asymmetric population of its p x̂ and p ŷ orbitals.