Electronic transitions, intensity polarization

In Figure 5.18 the absorption and emission spectra of azulene are shown. The anomalous fluorescence of azulene from the S, state is easy to recognize. The AP(F) spectrum exhibits a deep minimum at 33,900 cm. The small peak in the absorption spectrum at the same wave number is therefore not due to vibrational structure but rather to another electronic transition, the polarization of which had been predicted by PPP calculations. Figure 5.19 shows all four types of polarization spectra of phenanthrene. FP becomes negative at the vibrational maxima of the fluorescence the most intense vibration is not totally symmetric, in contrast to the one which shows up weakly. For all absorption bands, AP(P) = -0.3. The polarization direction of phosphorescence is perpendicular to the transition moments of all transitions lying in the mo-... 

A very weak peak at 348 mn is the 4 origin. Since the upper state here has two quanta of v, its vibrational syimnetry is A and the vibronic syimnetry is so it is forbidden by electric dipole selection rules. It is actually observed here due to a magnetic dipole transition [21]. By magnetic dipole selection rules the A2- A, electronic transition is allowed for light with its magnetic field polarized in the z direction. It is seen here as having about 1 % of the intensity of the syimnetry-forbidden electric dipole transition made allowed by... 

The photoelectric cross-section o is defined as the one-electron transition probability per unit-time, with a unit incident photon flux per area and time unit from the state to the state T en of Eq. (2). If the direction of electron emission relative to the direction of photon propagation and polarization are specified, then the differential cross-section do/dQ can be defined, given the emission probability within a solid angle element dQ into which the electron emission occurs. Emission is dependent on the angular properties of T in and Wfin therefore, in photoelectron spectrometers for which an experimental set-up exists by which the angular distribution of emission can be scanned (ARPES, see Fig. 2), important information may be collected on the angular properties of the two states. In this case, recorded emission spectra show intensities which are determined by the differential cross-section do/dQ. The total cross-section a (which is important when most of the emission in all direction is collected), is... 

Anthracene absorbs at two wavelengths, at 360 nm and at 260 nm. The flat molecule is anisotropic and it has long axis along x coordinates and a short axis along y coordinate. The absorption at 360 nm is short axis polarized (La type). A substituent at 9,10 or 1, 4, S, and 8 positions may help rr retard the creation of dipole in this direction. Therefore, the intensity or position of this absorption region may be influenced by such substitutions. The absorption at 260 nm is long axis polarized (Lb type) and is perturbed by substitution at 2, 3, 6 and 7 positions. Such substituent effects are sometimes used to identify the polarization directions of a given electronic transition. 

The N3 and NNO molecules are linear. What are the ground-state terms What are the designations of the excited states which arise on the lowest energy electronic transition Discuss the intensities and polarizations that might be anticipated for the bands. 

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