Experimental spectroscopy measured quantities and set-ups

Infrared Spectroscopy of H-Bonded Systems Theoretical Descriptions 

Following the approach of electromagnetism, we characterize the linear response of the medium to the electromagnetic field by a freqnency-dependent dielectric constant e. The induced electric dipole moment is equal to this dielectric constant mnltiplied by the value of the electric field of the irradiating electromagnetic wave, s is a complex quantity, having the form, with F = — 1 

The real part e of this dielectric constant characterizes that part of the dipole moment that is in phase with the electric field at a fixed position of the sample and therefore 

In optical spectroscopy, the properties of the medium are not defined by its complex dielectric constant e(v) (eq. (5. A3)) but by its optical complex constant 

The real part n of this optical constant is the well-known refractive index of the medium, while its imaginary part k is its absorption coefficient. The propagation of an optical wave inside the medium along axis z, for instance, is then defined by the propagation of its electric vector E as 

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