Properties. ESR Spectrum

Further ab Initio [5, 6, 11, 12] and semlempirical [8, 12, 13] calculations gave somewhat differing geometrical parameters. 

Ab Initio calculations showed that the TBP-eq form is energetically favored by about 80 kJ/mol over the TBP-ax structure (Cg symmetry, missing ligand In axial position) [5, 6,11]. An even higher Instability relative to the TBP-eq form resulted for square pyramid (Cs or C4J [11], square-planar (D4h) [11], and tetrahedral (T, ) [11, 14] structures of PH4. 

An ab initio study of the pathway of ligand scrambling of PH4 indicated a turnstile mechanism Involving a TBP-ax transition state with a lower barrier than a Berry pseudorotation process with a C4V transition state [11] see [7]. 

The electron affinity of PH4 predicted by ab initio calculations (UMP2 procedure) to be A= 0.60 0.05 eV [18]. 

An analysis of the ESR spectra of PH4 (and deuterated species) in xenon and neopentane matrices confirmed the theoretically obtained TBP-eq structure of PH4 [1 to 3, 23]. The best resolved ESR spectrum of PH4 was observed In a neopentane matrix [2]. The spectrum at 100 K consists of eight 0.6 mT triplets (1 2 1). The large Interaction of -50 mT was due to a P nucleus, and the smaller (-0.6 and 20 mT) interactions were due to pairs of equivalent protons. The ESR spectrum of PD4 In neopentane-di2 consisted of a pair of 3 mT quintets (1 2 3 2 1) arising from hyperfine interactions with a 3i p nucleus and two equivalent deuter-ons [3]. Anisotropic features in the spectrum of PH4 in a xenon matrix at 4.2 K were Interpreted in terms of fast torsional oscillations about the symmetry axis of PH4 [2]. The following g fac- 

---