Electronic spectra blue shift

The p3/2 spectrum of Be-II shows no evidence of a split ground state and it has been suggested that this centre could be a pair of nn substitutional Be atoms (Be2), whose trigonal symmetry has been confirmed by the piezospectroscopic measurements of [77], It may be seen [45] as a divacancy V2 into which two Be atoms are placed the two valence electrons of each Be atom satisfies four of the six dangling bonds of V2 and the two remaining bonds are completed by two electrons of the VB, leaving two holes. Within this scheme, the Be2 pair should then be a double acceptor. An unusual feature is the observation of a much weaker replica of the main spectrum, blue-shifted by... 

Pulse radiolysis provides also means to determine the size of chemically prepared CdS clusters in measuring their reaction rate with OH radicals. The mechanisms of such an electron transfer process from the surface of CdS, CdTe and ZnTe, PbS semiconductor particles to OH radicals, and from solvated electrons or alcohol radicals to the particle were studied. The absorption spectrum of CdS with an excess electron is blue-shifted. Colloidal nanoparticles (2 nm) of chalcopyrite CuFeSj are oxidized in their first monolayer by Fe "ions induced by a pulse. 

Chemiluminescence is believed to arise from the 2Bj and the 2B2 electronic states, as discussed above for the reaction of NO with ozone [17]. The primary emission is in a continuum in the range =400-1400 nm, with a maximum at =615 nm at 1 torr. This emission is significantly blue-shifted with respect to chemiluminescence in the NO + 03 reaction (Xmax = 1200 nm), as shown in Figure 2, owing to the greater exothermicity available to excite the N02 product [52], At pressures above approximately 1 torr of 02, the chemiluminescence reaction becomes independent of pressure with a second-order rate coefficient of 6.4 X 10 17 cm3 molec-1 s-1. At lower pressures, however, this rate constant decreases and then levels off at a minimum of 4.2 X 1(T18 cm3 molec-1 s-1 near 1 mtorr, and the emission maximum blue shifts to =560 nm [52], These results are consistent with the above mechanism in which the fractional contribution of (N02 ) to the emission spectrum increases as the pressure is decreased, therefore decreasing the rate at which (N02 ) is deactivated to form N02. Additionally, the radiative lifetime and emission spectrum of excited-state N02 vary with pressure, as discussed above for the NO + 03 reaction [19-22],... 

An effect observed in the spectrum of a chemical species in which a substituent, solvent, change in environment, or other effect causes the electronic absorption spectrum to shift to shorter wavelengths. The opposite effect is referred to as a bathochromic shift. The hypsochromic shift is also known as the blue shift. 

Examination of the optical spectrum of the filtered purple solution gave a structured absorption band with maxima at 514 and 543 nm. This position is remarkably close (566 nm) to the n-n electronic transition predicted by Davis and Goddard for the parent system H2N=N. As expected for an n-n transition, the position of the absorption maximum is solvent dependent. In dichloromethane solution, A,i ax is 541 nm, in 2-propanol it is 526 nm. The blue shift of 15 nm is completely consistent with the n-n absorptions of isoelectronic carbonyl compounds. 

Cadmium sulfide suspensions are characterized by an absorption spectrum in the visible range. In the case of small particles, a quantum size effect (28-37) is observed due to the perturbation of the electronic structure of the semiconductor with the change in the particle size. For the CdS semiconductor, as the diameter of the particles approaches the excitonic diameter, its electronic properties start to change (28,33,34). This gives a widening of the forbidden band and therefore a blue shift in the absorption threshold as the size decreases. This phenomenon occurs as the cristallite size is comparable or below the excitonic diameter of 50-60 A (34). In a first approximation, a simple electron hole in a box model can quantify this blue shift with the size variation (28,34,37). Thus the absorption threshold is directly related to the average size of the particles in solution. 

---