Temperature effects on positive hole scavenging in methanol investigated by positron annihilation techniques

The temperature effects on the enhancement of positronium (Ps) formation promoted by various solutes are investigated in methanol using both the lifetime spectroscopy and the Doppler broadening of the annihilation radiation lineshape techniques. The solutes are: n-propylamine (PA), triethylamine (TEA), allylamine, aniline, N-N dimethylaniline (DMA), hydroquinone and hexamethylphosphorotriamide (HMPT). On basis of the spur model, the enhancement is attributed to hole scavenging by the solutes. However, the combined use of the two experimental techniques shows that the solutes also inhibit Ps formation by positron scavenging. The temperature effects on Ps enhancement are rather small by contrast with those on limited inhibition, suggesting the presence of mobile holes in the solvent. (author)