Absorption-like line shape

On pp. 31 Iff., a preliminary discussion of the symmetry of induced line profiles was given. The spectral lines encountered in collision-induced absorption show a striking asymmetry which is described roughly by a Boltzmann factor, Eq. 6.59. However, it is clear that at any fixed frequency shift, the intensity ratio of red and blue wings is not always given exactly by a Boltzmann factor, for example if dimer structures of like pairs shape the profile, or more generally in the vibrational bands. We will next consider the latter case in some detail. 

As discussed in connection with IR absorption, Raman lines from a discrete transition may also assume Fano type shapes if the transition is coupled to a continuum of scattering states. This continuum may originate from various sources like, for example, electronic or two phonon excitations. In general, Raman scattering makes it even easier to observe Fano lines, since the free carrier response very often covers up details of the line shape in IR reflection. Similarly, such line shapes have so far only been shown by classical semiconductors and most recently by superconductors, and it is a challenge to search for them in other conducting organic systems. 

The resolution of rhombic g-factors in powder spectra of apparent axial symmetry spectra at low frequency can be more easily obtained for species having larger -anisotropy as schematically shown in Fig. 4.5 using parameters for the carbon dioxide radical, C02 , with g =2.0032, gy = 2.0014, gz =1.9975 obtained from single crystal measurements. The powder spectrum at X-band shows an apparent axial symmetric spectrum shape. With a typical line-width of ca 0.2-0.4 mT, the gn and gy features are resolved already at Q-band. The anisotropic g-factors can be directly measured at the absorption-(gx) and emission-(gz) like lines and at the centre (gy) of the 1st derivative Q-band spectrum. 

RMieS-EMSC correction has completely removed the oscillating baseline and the derivative-line shape that was present at the amide I band. As a result, the position of the amide I band has shifted from 1641 to 1654 cm which is likely to be very close to the true position of this absorption band. ... 

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