Coincidence Doppler broadening study of polar and nonpolar molecules in liquid and solid states

We demonstrate that coincidence Doppler broadening (CDB) spectroscopy appears to be promising for studying positron solvation and positronium bubble formation in liquids. Significant positron trapping by oxygen was observed in polar cyclohexanone (C6H10O) and ethanol (C2H5OH), and the oxygen effect is stronger in liquid state than that in solid state. Such difference could be attributed to the positron solvation effect. It is also shown that positronium annihilation inside the bubbles formed in liquid n-hexane (C6H14) and cyclohexane (C6H12) leads to a significant broadening of CDB curves within the momentum region of ∼5–20 × 10−3m0c.