Temperature Dependence of Fluorescence Spectra

Gas spectra excited by EWs can also be influenced by atoms which are adsorbed on the surface. The adsorbate overlayer determines the boundary conditions for Maxwell s equations at the interface and, therefore, also the EW amplitude in the gas. As a result, the gas optical spectra which depend on the EW intensity, contain indirectly information about the adsorbed layer. In particular, the atoms adsorbed on the surface are polarized by the exciting field, 

For small surface coverages, when the effect of the local field can be neglected, the adsorbate polarization, Ps, is expressed in terms of the adatom dynamic polarizability, iXs co), as 

o is the tangential component of the electric field amplitude at the interface and Ns is the surface number density of adsorbed atoms. It is also assumed that the dielectric response of the adsorbed atoms is isotropic in the surface plane. Accounting for the surface current (7.43) in the boundary condition for the tangential components of the magnetic field, results in a modified expression for the transmitted field amplitude. For example, in the case of s-polarization one obtains, instead of Eq. (3.13) with 62 = 1, 

This equation is valid also for the case of total internal reflection provided that 6i exceeds the critical angle. It relates the EW amplitude to the surface coverage, 6, defined in terms of Ng. In the framework of the Langmuir model of adsorption the quantity is related to the surface temperature by Eqs (2.146), (2.144) and (2.145). Therefore, measuring the EW fluorescence spectra from the gas as a function of surface temperature allows one to obtain information on the adsorbate. 

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