Vibrational relaxation of carbon dioxide (101) and carbon monoxide (v=2) during gas–surface collisions

Abstract

The probability for deactivation of CO(v=2) and CO₂(101) on collision with polycrystalline silver surfaces has been measured. The deactivation probability for CO(v=2) was found to decrease from 0.33 at 300 K to 0.20 at 440 K, while the deactivation probability for CO₂ (101) was found to decrease from 0.72 at 300 K to 0.37 at 440 K. Since no population was observed in the CO(v=1) and CO₂ (001) intermediate levels, it appears that each deactivation proceeds completely to produce the vibrational ground level. The magnitudes for the deactivation probabilities and the temperature dependencies indicate that a dominant mechanism for relaxation involves trapping and subsequent deactivation by one or more of several mechanisms, including electron–hole pair formation, vibration‐to‐rotation energy transfer, or perhaps even transfer of energy to the surface phonons. The experiments were performed in a UHV chamber by using a tunable infrared laser source to excite gas‐phase molecules vibrationally before their collision with the surface and by measuring the population of vibrationally excited molecules through their time‐resolved infrared fluorescence.