Temperature dependences of spectral line shifts and widths

Temperature dependences of spectral line shifts and widths 

Treating vibrational excitations in lattice systems of adsorbed molecules in terms of bound harmonic oscillators (as presented in Chapter III and also in Appendix 1) provides only a general notion of basic spectroscopic characteristics of an adsorbate, viz. spectral line frequencies and integral intensities. This approach, however, fails to account for line shapes and manipulates spectral lines as shapeless infinitely narrow and infinitely high images described by the Dirac -functions. In simplest cases, the shape of symmetric spectral lines can be characterized by their maximum positions and full width at half maximum (FWHM). These parameters are very sensitive to various perturbations and changes in temperature and can therefore provide additional evidence on the state of an adsorbate and its binding to a surface. 

This wide range of questions is to be elucidated in the present chapter. The bulk of attention is given to the effects induced by the collectivization of adsorbate vibrational modes whose low-frequency components are coupled to the phonon thermostat of the substrate. This coupling gives rise to the resonant nature of low-frequency collective excitations of adsorbed molecules (see Sec. 4.1). A mechanism underlying the occurrence of resonance (quasilocal) vibrations is most readily 

Resonant nature of low-fiequency collective excitations of adsorbed molecules 

---

In the pivotal Chapter 4, temperature dependences of spectral line shifts and widths are analyzed. To treat them, we have to invoke rather complex concepts of... 

---