Positronium formation studies in solid molecular complexes: Triphenylphosphine oxide–triphenylmethanol

Positronium formation in triphenylphosphine oxide (TPPO), triphenylmethanol (TPM), and systems [TPPO(1−X)⋅TPMX] has been studied. The low probability of positronium formation in complex [TPPO0.5⋅TPM0.5] was attributed to strong hydrogen bond and sixfold phenyl embrace interactions. These strong interactions in complex reduce the possibility of the n- and π-electrons to interact with positrons on the spur and consequently, the probability of positronium formation is lower. The τ3 parameter and free volume (correlated to τ3) were also sensitive to the formation of hydrogen bonds and sixfold phenyl embrace interactions within the complex. For physical mixture the positron annihilation parameters remained unchanged throughout the composition range.