非常态分子CH_4在稀土La薄膜不同表面温度下的激活化学吸附

STUDIES OF ACTIVATED CHEMISORPTION OF ANOMALOUS MOLECULAR CH_4 ON La FILM UNDER DIFFERENT TEMPERATURES

本文用分子束改变平动能的方法，研究了非常态分子ＣＨ４在处于不同表面温度下的稀土Ｌａ薄膜上的激活化学吸附。实验结果表明，当非常态分子的平动能在１０．１～６４．０ｋＪ／ｍｏｌ（对应的垂直分量在７．５～４８．１ｋＪ／ｍｏｌ）之间变化时，只有能量大于５２．３ｋＪ／ｍｏｌ（垂直分量为３９．３ｋＪ／ｍｏｌ）的分子才发生化学吸附，此值称为阈值。当非常态分子的平动能超过阈值时，初始粘着几率Ｓ０随平动能的增大而线性增加。当样品表面温度由５００Ｋ升至７００Ｋ时，虽然样品表面温度升高，但ＣＨ４的阈值能没有改变，且表面的活化能也没有改变。由此说明，阈值能和活化能与样品表面温度无关，它主要由作用于表面上的气体及表面的结构和性质决定。

The activated chemisorption of CH4 on La film has been studied. It is found that the initial sticking probability S0 depended on the incident energy E, scaling En= Ecos2θ. No activated chemisorption was observed for CH4/La below En =39. 3kJ/mol at surface temperature from 500K to 700K. Above En= 39. 3kJ/mol, the initial sticking probability S0 increases linearly from 0 to 49%, 42% and 35% at surface temperature of 500K, 600K,700K respectively. But threshold value and the activated energy remain constant as surface temperature is changed.