物理化学学报 >> 1985, Vol. 1 >> Issue (01): 39-48.doi: 10.3866/PKU.WHXB19850106

研究论文 上一篇    下一篇

超高真空质谱法研究氧在电解银上的吸附态

邓景发; 包信和; 郭伯麟   

  1. 复旦大学化学系
  • 收稿日期:1984-07-21 修回日期:1984-10-10 发布日期:1985-02-15

THERMAL DESORPTION MASS SPECTROMETRY OF OXYGEN CHEMISORBED ON ELECTROLYTIC SILVER UNDER UHV

Deng Jingfa; Ban Xinhuo; Guo Bailin   

  1. Chemistry Department; Fudan University
  • Received:1984-07-21 Revised:1984-10-10 Published:1985-02-15

摘要:

运用超高真空程序升温反应(TPRS)技术研究了氧在电解银上的化学吸附。在宽广的压力范围内(1—10~(-8) torr)考察了几种吸附氧种的变化规律, 并观察到在覆盖度为0.2—0.6时表面吸附物种的突变。用同位素交换和CO滴定实验证实了在电解银表面存在三种氧吸附态: (1) 弱的未解离的分子态吸附(E_d=92 kJ mol~(-1), v=4×10~(11) S~(-1)); (2) 强的解离的原子态吸附(E_d=134 kJ mol~(-1), v=4.7×10~(13) S~(-1)); (3)氧在银体相中扩散。进一步的实验发现, 分子态吸附氧与表面杂质的存在有关。用等温脱附技术研究了氧在银中的扩散, 得到了扩散量随温度增加的定性规律。

Abstract:

Thermal desorption spectra for oxygen chemisorbed on electrolytic silver have been obtained using a temperature programmed reaction (TPRS)technique with mass analysis in an ultrahigh vacuum (UHV) system. More than twenty times cycles of pretreatments were carried out at a partial pressure of oxygen equal to 1×10~(-3) torr and at 650 ℃ while desorption measurements were obtained in a total pressure enviroment 2-5×10~(-9) torr. For oxygen exposure 90 L three distinct species appear in the desorption spectra. Isotope-mixing, CO titration and kinetic behaviour studies lead to the following assignments: weakly molecularly chemisorbed oxygen (E_d=92 kJ mol~(-1), v=4.1×10~(11) s~(-1)), strongly chemisorbed stomic oxygen (E_d=134 kJ mol~(-1), v=4.7×10~(13) s~(-1)) and oxygen diffused to the bulk of silver (see Fig.2). Detailed information about the variation of states of adsobed oxygen with exposure, between 5 L and 10~8 L, have been obtained and for θ=0.2~0.6 a “break” of atomic oxygen desorption is also found, in agreement with other studies. The desorption of molecularly adsorbed oxygen exhibited complex kinetics due to lateral interactions between the adsorbed molecularly oxygen and stomic oxygen. It is suggested that the adsorption of molecularly oxygen due to the presence of surface impurities, such as sodium, carbon, sulfur etc.. The behavior of the desorption of bulk oxygen has been studied by isothermal dessorption technique. The result shows that the higher temperature of oxygen adsorption favors the diffusion of oxygen.