Excitation energy vertical

All of the predicted excitation energies are in good agreement with the experimental values. It should also be noted that the experimental excitation energy for the third state measured the adiabatic transition rather than the vertical transition, so this value must be assumed to be somewhat lower than the true vertical excitation energy. A larger basis set is needed to produce better agreement with experiment. 

Figure 3 Frequency-dispersion curves of the longitudinal polarizability per unit cell of infinite periodic chains of hydrogen molecules according to the method used (RPA (bottom) and UCHF (top)). AH the values are in a.u.. The position of the first excitation energies which corresponds to the poles is indicated by vertical bars.

Figure 1.3. Real-time femtosecond spectroscopy of molecules can be described in terms of optical transitions excited by ultrafast laser pulses between potential energy curves which indicate how different energy states of a molecule vary with interatomic distances. The example shown here is for the dissociation of iodine bromide (IBr). An initial pump laser excites a vertical transition from the potential curve of the lowest (ground) electronic state Vg to an excited state Vj. The fragmentation of IBr to form I + Br is described by quantum theory in terms of a wavepacket which either oscillates between the extremes of or crosses over onto the steeply repulsive potential V[ leading to dissociation, as indicated by the two arrows. These motions are monitored in the time domain by simultaneous absorption of two probe-pulse photons which, in this case, ionise the dissociating molecule.

For C3H2 to be identified in space from its UV -VUV spectra, one needs to know reliable values of its low vertical electronic excitation energies. For that purpose, a number of experimental studies [30] have been realized in an attempt to observe C3H2 electronic transitions between 2000 and 6000 A. These experiments having failed, computational chemistry is the alternative left to search for stable electronic states, if any, which might have been overlooked in the region between 2 and 6 eV. 

Table 7 Vertical excitation energies for the two lowest excited states of C2H4...

No significant improvement for the vertical excitation energy of the 2 B (3p) state was found. From these results we have decided to describe the lowest states of B and A2 symmetries with the same set of molecular orbitals, optimized for the neutral molecule within the MCSCF/ 6422 expansion. 

Our best estimation for the vertical excitation energies for states of A, symmetry are reported in Table 12. They correspond to a ground state calculated at CI( 6) level using orbitals optimized for the neutral molecule with the MCSCF/SD expansion, and excited Rydberg states calculated at the level using orbitals optimized for the positive ion... 

Vertical excitation energies to states of B symmetry, calculated at the level using the orbitals optimized for the neutral molecule with the MCSCF/6422 expansion, are reported Table 12. The I Bi valence state and 2 B (3p) Rydberg state of C3H2 are respectively 5.2 eV and 7.5 eV above the ground state with large transition moments of... 

Table 11-1. Vertical excitation energies in eV relative to the ground state minimum of the singlet electronic excited states in the uracil...

Table 11-6. Vertical excitation energy shifts in eV for uracil and thymine in aqueous phase compared to gas phase, using various levels of theory. The ordering of the states is according to the gas phase energies...

These studies discuss vertical and adiabatic excitation energies but the photophysical behavior requires calculations along the PES and at highly distorted geometries, which are more difficult to carry out in the presence of solvent. Some theoretical work has been done in this area, but it is quite limited. 

Poly(aminoborane) has a relatively simple structure, as shown in Figure 9. Jacquemin and co-workers [63] performed a comprehensive set of calculations to investigate the infrared spectra, vertical excitation energies, geometries, atomic charges and dipole moments as a function of conformation. A variety of theoretical methods were employed, including Hartree-Fock, MP2 and... 

TABLE 6. CASPT2 vertical excitation energies (eV) for the low-lying excited states of butadiene, hexatriene and octatetraene0... 

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