“…Other examples of Rydbergization have been reported in the lowest 3s Rydberg states of diatomic hydrides as NH and CH, , OH, , and in the isoelectronic N 2 molecule . To our knowledge this is the first quantitative description of such a Rydbergization in a tetra-atomic molecule like C 2 H 2 although computational aspects can be found in ref .…”
A quantitative characterization of the Rydberg and valence singlet electronic states of acetylene lying in the 5-10.7 eV region is performed by using large-scale ab initio calculations. A special attention is paid on the comparison between the present calculations and Mulliken's concepts for Rydberg states, based on single-electron and single-configuration description. Most of the properties of the Rydberg states have been qualitatively understood via this comparison, mainly shown by the shape and size of the outer Rydberg molecular orbital. More quantitatively, Rydberg-valence mixing has been evaluated in several excited energy regions, as for instance, the interaction between the ' (1pig)2 1Ag doubly excited valence state and the manifold of electronic components of the np series, or the interaction between the 1pig 1Bu valence state and the 3dpig 1Sigma(u)+ Rydberg state. The rapid predissociation of the lowest 3s(sigma) 1Piu Rydberg state has been interpreted as a case of Rydbergization, earlier predicted by Mulliken.
“…Other examples of Rydbergization have been reported in the lowest 3s Rydberg states of diatomic hydrides as NH and CH, , OH, , and in the isoelectronic N 2 molecule . To our knowledge this is the first quantitative description of such a Rydbergization in a tetra-atomic molecule like C 2 H 2 although computational aspects can be found in ref .…”
A quantitative characterization of the Rydberg and valence singlet electronic states of acetylene lying in the 5-10.7 eV region is performed by using large-scale ab initio calculations. A special attention is paid on the comparison between the present calculations and Mulliken's concepts for Rydberg states, based on single-electron and single-configuration description. Most of the properties of the Rydberg states have been qualitatively understood via this comparison, mainly shown by the shape and size of the outer Rydberg molecular orbital. More quantitatively, Rydberg-valence mixing has been evaluated in several excited energy regions, as for instance, the interaction between the ' (1pig)2 1Ag doubly excited valence state and the manifold of electronic components of the np series, or the interaction between the 1pig 1Bu valence state and the 3dpig 1Sigma(u)+ Rydberg state. The rapid predissociation of the lowest 3s(sigma) 1Piu Rydberg state has been interpreted as a case of Rydbergization, earlier predicted by Mulliken.
“…Aniline in the low pH regime shows two low-energy absorption bands at 260 and 254 nm. In the high pH regime, aniline exhibits two broad absorption features centered at 280 and 230 nm corresponding to 1 L b and 1 L a states. , For both aniline and indoline, the increased absorption strength and longer absorption wavelength in the high pH regime can be attributed to resonance structures extending conjugation to the nitrogen atom. In the low pH regime, the hybridization of the protonated nitrogen (>NH 2 + ) eliminates contributions from these resonance structures.…”
This paper presents a detailed description of the fluorescence and photophysical behavior of indoline and
indoline-2-carboxylic acid (I2CA). Indoline is an analogue of indole lacking the C2C3 double bond, but
unlike indole, indoline possesses well-separated 1La and 1Lb states. I2CA, which displays similar fluorescence
properties, is an amino acid and can be regarded as a fluorescent analogue of proline. In view of the potential
for indoline and I2CA as fluorescent probes in peptides and proteins, we have undertaken an in-depth study
of the spectroscopic and photophysical properties of these molecules. A companion paper (Slaughter, B.D.;
Allen, M. W.; Lushington, G. H.; Johnson, C. K. J. Phys. Chem. A
2003, 107, 5670) presents a theoretical
treatment of the spectroscopic transitions of indoline and I2CA. The pH-dependent absorption and fluorescence
characteristics are investigated for both indoline and I2CA. Ground- and excited-state dissociation constants
are determined spectroscopically. Quantum yields and radiative lifetimes are reported, and relaxation
mechanisms are explored for both indoline and I2CA. Comparisons are made to the model systems of aniline
and indole. The fluorescence lifetime of indoline is 4 to 7 ns in nonaqueous solvents but is reduced to 0.18
ns in water by electron-transfer quenching. The fluorescence decays of I2CA indicate the presence of two
conformations, one with a short (<1 ns) lifetime and the other with a lifetime of 4 to 5 ns in most solvents.
The fluorescence properties of I2CA in water are unvaried from pH 6−10 with a fluorescence decay component
of 5.0 ns that makes it useful as a potential fluorescence probe.
“…The electronic transitions of aniline have been used here as a basis of comparison for indoline and I2CA. The 1 L a and 1 L b transitions of aniline have been well studied elsewhere. − 5 Transition densities for aniline and indoline. The bottom and top rows display the transition density for the 1 L b and 1 L a transitions, respectively.…”
In this study, a range of computational methods including time-dependent density functional theory, configuration interaction, and Zerner's spectroscopic intermediate neglect of differential overlap are used to classify spectroscopic properties of indoline and indoline-2-carboxylic acid. By examining transition densities, the 1 L a and 1 L b states of indoline and indoline-2-carboxylic acid are assigned. Aniline is used as a reference system. Excitation energies, oscillator strengths, dipole moments, and transition dipoles have been calculated and are found to be in close agreement with experiment. We find that the electronic transitions of indoline are similar to those for aniline. The lowest excited singlet state in indoline, as in aniline, is the 1 L b state with a low oscillator strength. The 1 L a state is higher in energy and possesses a larger oscillator strength as well as a larger dipole moment. For indoline-2-carboxylic acid, 1 L b -and 1 L a -like states can be identified, but an evaluation of their properties reveals mixed 1 L a and 1 L b character. Ground-state energies for conformations of indoline-2-carboxylic acid differing in the orientation of the carboxylic group indicate the presence of two ground-state conformations of similar energy.
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