Interaction of Atomic Oxygen with Various Surfaces

A pulsed atomic-oxygen beam is used to investigate the interaction of atomic oxygen with various surfaces at a pressure of 10−7 torr. The probability that an atom after striking a surface will return to the gas phase as an atom is measured for Pyrex, stainless steel, Teflon, gold, and titanium and is found to lie between 45% and 60% for all of these materials at room temperature. This reflection probability β is strongly temperature dependent for metals, dropping below 10% at 450°C, but less so for Pyrex, dropping only to 33% at the same temperature. The atoms which are not reflected apparently stick to the surfaces. In particular there is no evidence that at 10−7 torr they recombine to form O2 or are emitted as parts of oxygen-containing molecules such as CO2 or N2O. Qualitative experiments indicate that recombination does take place at pressures near 1 torr.