Electronic absorption spectra energy

One group has successfiilly obtained infonnation about potential energy surfaces without measuring REPs. Instead, easily measured second derivative absorption profiles are obtained and linked to the fiill RRS spectrum taken at a single incident frequency. In this way, the painstaking task of measuring a REP is replaced by carefiilly recording the second derivative of the electronic absorption spectrum of the resonant transition [, 59],... 

The preceding empirical measures have taken chemical reactions as model processes. Now we consider a different class of model process, namely, a transition from one energy level to another within a molecule. The various forms of spectroscopy allow us to observe these transitions thus, electronic transitions give rise to ultraviolet—visible absorption spectra and fluorescence spectra. Because of solute-solvent interactions, the electronic energy levels of a solute are influenced by the solvent in which it is dissolved therefore, the absorption and fluorescence spectra contain information about the solute-solvent interactions. A change in electronic absorption spectrum caused by a change in the solvent is called solvatochromism. 

Fig. 9. Calculated relative energies (in kK) of the most important MO s (a) and spectral excitation energies derived from the electronic absorption spectrum (b) of ClFe(Et2

FIGURE 2.1 Energy of the 0-0 vibrational transition in the principal electronic absorption spectrum of violaxanthin (l Ag-—>1 BU+), recorded in different organic solvents, versus the polarizability term, dependent on the refraction index of the solvent (n). The dashed line corresponds to the position of the absorption band for violaxanthin embedded into the liposomes formed with DMPC (Gruszecki and Sielewiesiuk, 1990) and the arrow corresponds to the polarizability term of the hydrophobic core of the membrane (n = 1.44). 

Absorption spectra can provide information relating to the energy of an excited singlet state. This corresponds to the lowest 0-0 vibrational transition in the electronic absorption spectrum. When the vibrational fine structure is evident, the energy of the excited singlet state is readily determined, but when the 0-0 band cannot be located, the value can be taken from the region of overlap of the absorption and fluorescence spectra. 

The recently available IR data138 for 8 indicate a C—O stretch at 1869 cm"1 and a ring stretch at 1591 cm 1. These compare with ah initio calculated values of 1869 and 1613 cm"1. The electronic absorption spectrum was also measured, assigned and compared with that calculated. The A2 (n7t ) symmetry forbidden band is centred at 344 nm, the A, (nn ) band at 274 and the lB2 (nn ) bands at 223 and 193 nm, respectively. In comparison to cyclobutabenzene-l,2-dione, the UV bands of 8 are shifted slightly to higher energies (ca 6 nm)138. 

This expression for the complete overlap is Fourier transformed to give the electronic emission spectrum. In order to carry out the calculation it is necessary to know the frequencies and the displacements for all of the displaced normal modes. In addition, the energy difference between the minima of the two potential surfaces E0 and the damping r must be known. As will be discussed below, the frequencies and displacements can be experimentally determined from pre-resonance Raman spectroscopy, and the energy difference between the ground and excited states and the damping can be obtained from the electronic absorption spectrum and/or emission spectrum. 

Since the suggestion of the sequential QM/MM hybrid method, Canuto, Coutinho and co-authors have applied this method with success in the study of several systems and properties shift of the electronic absorption spectrum of benzene [42], pyrimidine [51] and (3-carotene [47] in several solvents shift of the ortho-betaine in water [52] shift of the electronic absorption and emission spectrum of formaldehyde in water [53] and acetone in water [54] hydrogen interaction energy of pyridine [46] and guanine-cytosine in water [55] differential solvation of phenol and phenoxy radical in different solvents [56,57] hydrated electron [58] dipole polarizability of F in water [59] tautomeric equilibrium of 2-mercaptopyridine in water [60] NMR chemical shifts in liquid water [61] electron affinity and ionization potential of liquid water [62] and liquid ammonia [35] dipole polarizability of atomic liquids [63] etc. 

The electronic absorption spectrum of a catalyst shows which excitation energies will lead to resonance or far-from-resonance conditions (Clark and Dines, 1986 Nafie, 2001), the latter being common for colorless samples that have no electronic states in close proximity to the incident photon energy. If the incident photon energy is near the transition energy of an excited electronic state, the Raman scattering will change... 

The room temperature solution electronic absorption spectrum of (L-N3) MoO(bdt) is presented in Fig. 6. This spectrum is representative of virtually all (L-A i)MoO(dithiolene) complexes (19, 23) with the possible exception of (L-/Vi)MoO(qdt) (20, 22), where qdt = quinoxaline-2,3-dithiolate, see below. However, the transitions observed for (L-A MoChtdt) (19), where tdt = toluene-1,2-dithiolate, are generally shifted to slightly lower energies relative... 

Figure 24 displays the high energy (E > 25,000 cm-1) region of the room temperature electronic absorption spectrum for Zn(bpy)(tdt), where bpy = 2,2 -bipyridine. The LLCT transition occurs at 22,470 cm-1 (445 nm) with very weak absorption intensity (e = 72 M 1cm 1). The origin of the weak LLCT is a function of the symmetry of this psuedo-tetrahedral complex. A MO diagram for Zn(bpy)(tdt), derived from extended Hiickel calculations, is presented in Fig. 25. Irrespective of whether the metallo(diimine)(dithiolene) complex is square-planar or psuedo-tetrahedral, the point symmetry is C2V, and all intermediate geometries possess C2 symmetry. When the dithiolene and diimine planes are orthogonal (psuedo-tetrahedral geometry) the HOMO — LUMO transition represents a b2 —> b one-electron promotion and is electric dipole forbidden. However, the HOMO —> LUMO transition in a square-planar...

Figure 2. Excited-state spectral features ofD -CuCl/-. A Energy level diagram showing the ligand-field (d - d) and charge-transfer (CT) optical transitions. The intensity of the transitions is approximated by the thickness of the arrow with the very weak ligand-field transitions represented as a dotted arrow. B Electronic absorption spectrum for D4h-CuCl42 (12). C Schematic of the a and tt bonding modes between the Cu 3dx2 y2 and Cl 3p orbitals.

There have been detailed studies on the electronic absorption spectrum of the gas, and the magnetic circular dichroism spectrum has also been recorded and assigned 577,578,580 such spectra were also obtained for the aqueous solution.581 The electronic spectrum of the solid in an argon matrix at 20 K was measured and assigned.580 An energy level diagram was constructed on the basis of the... 

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