P Polarisation

Lizlovs, E. A. and Bond, A. P., Polarisation Behaviour of High-purity 13 and 18% Chromium Stainless Steels , J. Electrochem. Soc., 119, 219c (1972)... 

In EMIRS and SNIFTIRS measurements the "inactive" s-polarlsed radiation is prevented from reaching the detector and the relative intensities of the vibrational bands observed in the spectra from the remaining p-polarised radiation are used to deduce the orientation of adsorbed molecules. It should be pointed out, however, that vibrational coupling to adsorbate/adsorbent charge transfer (11) and also w electrochemically activated Stark effect (7,12,13) can lead to apparent violations of the surface selection rule which can invalidate simple deductions of orientation. 

We assume that, on formation of B- XY, a fraction 5j (i = intermolecular) of an electronic charge is transferred from the electron donor atom of Z of the Lewis base B to the npz orbital of X and that similarly a fraction 5p (p = polarisation) of an electronic charge is transferred from npz of X to n pz of Y, where z is the XY internuclear axis and n and n are the valence-shell principal quantum numbers of X and Y. Within the approximations of the Townes-Dailey model [187], the nuclear quadrupole coupling constants at X and Y in the hypothetical equilibrium state of B- -XY can be shown [178] to be given by ... 

In applying RAIRS to CO adsorption, the contribution from CO molecules in the gas phase to the absorption spectrum at CO pressures above 10-3 mbar completely obscures the weak absorption signal of surface adsorbed CO. Beitel et al. found it possible to subtract out the gas phase absorption by coding the surface absorption signal by means of the polarization modulation (PM) technique applied to a conventional RAIRS spectrometer, p-polarised light produces a net surface electric field which can interact with adsorbed molecules, whereas both polarization states are equally sensitive to gas phase absorption because gas phase molecules are randomly oriented. By electronic filtering a differential spectrum is computed which does not show contributions from the gas phase and which has much higher surface sensitivity than a conventional RAIRS setup. 

P polarisation, nett dipole moment densities per unit volume... 

Figure 2.41 The direction of the electric vector for light polarised in the S- and P-directions before being incident at a planar surface at an angle 6, and the resolution of the electric vector of the P-polarised light into its components parallel and perpendicular to the reflective surface.

P-polarised light can be reduced to two components Px polarised parallel to the surface and Ps polarised perpendicular to the surface. The Px component also suffers a 180° phase change on reflection for all 9 and is thus blind to any surface species. However, the phase shift for the Pz component changes rapidly with 9. This results in the ratio of the standing wave/incident ray mean electric held strength, <( >/<( ,2 >, varying with 9 as shown in Figure 2.42. The above discussion has two important implications ... 

The surface selection rule operates in addition to the normal IR selection rules in determining which vibrational modes are observed. As a result of the SSR the relative intensities of the fundamental IR adsorption bands of an adsorbed species can be used to give information on the orientation of the species with respect to the surface. Both S- and P-polarised light interact equally with the randomly oriented solution species. 

Consider a linearly polarised monochromatic light ray incident on a metal surface. Such a ray can always be resolved into two orthogonal components and if the plane of reflectance at the metal is chosen as the reference, then these components correspond to S- and P-polarised light, as discussed in the previous section. 

Figure 2.59 The path followed by the tip of the electric vector of elliptically polarised light. ES, (1 and ,. ref show the directions of the planes of the S-potarised and P-polarised light. For...

Figure 2.60 Simple schematic representation of an ellipsometer. S = source, M = monochromator, P - polariser, E = reflective electrode, A = rotating analyser. D = detector.

Figure 5. The P-polarised emission spectrum obtained for hole injection by the thianthrene radical cation into Au(lll) for emission angle = 30° and excitation energy Eex = 3.0eV. (NB.

What happens to the diffracted beam in an anisotropic medium (e.g. as in an AOTF device) As given above, the birefringence induced by the acoustic wave causes the diffracted beam polarisation to change. So if, for example, the input beam is P-polarised, then... 

The probe was always p-polarised. The polarisation of the pump could be varied continuously from a p-polarised state either to a circularly polarised state by rotating a quarter wave plate (12) placed after a polarizer (13) (geometry 1), or to a state in which the beam was linearly polarized at an angle to the plane of incidence (geometry 2). In the latter case a quarter wave plate (12) was placed in front of the polarizer (13) in order to make the... 

If, on the other hand, in two non-absorbing media the light beam is polarised parallel to the plane of incidence (p-polarised) the reflectance is... 

Fig. 112. Block diagram of the experimental set-up for differential reflectance. L, light source K, order filter P, polariser M, monochromator Ch, chopper A, variable light attenuator Sref, reference mirror PM, photomultiplier V, V2, amplifiers LIA, lock-in amplifier DIV, divider.

As far as the basis set is concerned, increasing its quality from split valence to double zeta does not lead to any improvement of the situation a slight increase in the energy dificrence was found on going from a (14,9,6/9,5/6) set of primitives contracted to < 6,4,3/3,2/3 > for the iron atom, the first row atoms and the hydrogen atom respectively, to the (14,11,6/10,6/6) < 8,6,3/4,2/3 > basis set (14). The addition of a p polarisation function on the hydrogen atom decreased this value somewhat, down to 1.8 kcal/mol, but in every case the trans isomer remained the most stable one (14). 

CAS SCF calculations were therefore performed with the split valence basis set incremented by a p polarisation function on the hydrogen atoms. Two different sets of active orbitals were considered. The first one was designed to account for the d - n back donation and was therefore restricted to the n type valence orbitals. The three 3d orbitals, which are strongly occupied, were each correlated by two weakly occupied orbitals, owing to the mixed 4d and tt o character of these weakly occupied orbitals. This 3 + 6 set of active orbitals referred to as CAS SCF-6 is populated by 6 electrons. The second set, hereafter referred as CAS SCF-12, took into account both a and n correlation eficcts. Twelve electrons were correlated and... 

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