Strongly allowed transitions electric

Fig. 3). Note that optical transitions between the two configurations are parity allowed as electric-dipole transitions. The spin-selection rule is relaxed by spin-orbit coupling, the more so the higher the principal quantum number is. Due to selection rules on AJ, the transitions 1S0-3F0 and 1S0-3P2 remain strongly forbidden. The emission is due to the 3P0,i >1 o transition. Whether 3P0 or 3Pj is the initial level depends on their energy difference and the temperature.

Relaxation of the rules can occur, especially since the selection rules apply strongly only to atoms that have pure Russell-Saunders (I-S) coupling. In heavy atoms such as lanthanides, the Russell-Saunders coupling is not entirely valid as there is the effect of the spin-orbit interactions, or so called j mixing, which will cause a breakdown of the spin selection rule. In lanthanides, the f-f transitions, which are parity-forbidden, can become weakly allowed as electric dipole transitions by admixture of configurations of opposite parity, for example d states, or charge transfer. These f-f transitions become parity-allowed in two-photon absorptions that are g g and u u. These even-parity transitions are forbidden for one photon but not for two photons, and vice versa for g u transitions [46],... 

A mercury atom that was ionized by a weak electron beam was captured in a miniature Paul (radio frequency) trap that has internal dimensions of rQ s 466 pm and zQ s 330 pm. The rf trapping frequency was 21.07 MHz with a peak voltage amplitude of about 730 V. The ion was laser cooled by a few microwatts of cw laser radiation that was frequency tuned below the 6s Si -6p Pi electric dipole transition near 194 nm. When the Hg+ ion was cold and the 194 nm radiation had sufficient intensity to saturate the strongly allowed S-P transition, 2 x 10 photons/s were scattered. With our collection efficiency, this corresponded to an observed peak count rate of about 10 s-1 against a background of less than 50 s— -. 

Light absorbed by an atom or molecule excites it from the initial ground (or excited) state to a higher-energy excited state for low-intensity light, this occurs, provided that the various applicable quantum rules for the transition are satisfied (electric-dipole "allowed" transitions). If quantum rules "forbid" a transition, then the transition is either absent ("strongly forbidden transition") or very weak ("weakly allowed transition"). The "Jablonski"110 diagram (Fig. 3.16) depicts various forms of absorption and emission from... 

For a carbonyl group in a Cjv symmetry environment, such as in formaldehyde, the dipole approximation for the n- r transition yields JWo f > 0 and Mo f = 0. Although the transition is magnetically strongly allowed and polarized along the CO axis, it is electrically forbidden. The absorption therefore is of very weak intensity and the rotational strength is equal to zero. Perturbations by vibrations or by an achiral solvent can affect and to such an extent that a small nonzero electric dipole transition moment results but again this produces only a very small absorption intensity and... 

The absense of strong-coupling of peptide transitions with electric transition moments of the allowed transitions of the nitrobenzyl group could be due either to large distances and/or to absence of an ordered array of the side-chains (either in the left-handed or in the right-handed a-helical conformation). 

The well-known tetrahedral [Co(NCS)4]2 ion has continued to attract attention from analytical chemists, physical chemists, and spectroscopists. The inelastic electron tunneling (IET) spectrum of (Me4N)2[Co(NCS)4] was compared with IR and Raman spectra of the same complex.359 The vibrational bands due to the Me4N+ were prominent in all three spectra, but Coligand stretches were absent from the IET spectra. The lowest 4 42 4T2 electronic transition was strong in the IET spectrum but absent from the IR spectrum. The electric dipole allowed 4A2 4TX electronic transition was observed in both the IET and IR spectra and no fine structure was observed. Complex formation equilibria between Co11 and SCN- were studied calorimetri-... 

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