Vibrational excitation and surface reactivity: An examination of the ngr;3and 2ngr;3modes of CH4

摘要

The effect of vibrational excitation upon the chemisorption of methane on thin films of rhodium has been investigated. Vibrational modes of the gas are selectively excited by infrared radiation. The rate of reaction is measured by following the pressure decrease in a closed system containing CH4in contact with the metal surface. Neither irradiation with a Hendash;Ne laser at 3.39 mgr; to excite the ngr;3mode, nor using an arc source with wavelengths in the range overlapping 2ngr;3, produces any detectable changes in the rate. From these experiments we estimate that the reaction probability of CH4is 1times;10minus;4in the first excited state of ngr;3, and 7times;10minus;2in 2ngr;3. Other excitations must be involved in overcoming the barrier of quest;7 kcal/mole which has previously been found for the chemisorption of CH4on rhodium.