Infrared Emission Spectroscopy
A molecule in a vibrationally excited state has a certain probability of emitting infrared radiation in the presence or in the absence of incident electromagnetic radiation, resulting in induced and spontaneous emission, respectively. At room temperature (T ≃ 300K), the number of molecules in a first excited state is less than 1% of the population in the ground state, when the separation of energy levels is about 1000 cm−1, typical in the infrared. The population should be negligible in still higher states. In consequence, the induced infrared emission is much weaker than the (induced) absorption. However, the spontaneous infrared emission is stronger than the induced emission under the experimental conditions generally employed in observing surface species, as described in Section 2.1 of Chapter 2. The infrared emission spectrum of a thin film on a solid surface, therefore, may easily be observed at moderately elevated temperatures.
KeywordsEmission Spectrum Metal Surface Emission Intensity Vinyl Acetate Surface Species
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