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Comparison of the resonance-enhanced multiphoton ionization spectra of pyrrole and 2,5-dimethylpyrrole: Building toward an understanding of the electronic structure and photochemistry of porphyrins
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10.1063/1.3257681
/content/aip/journal/jcp/131/17/10.1063/1.3257681
http://aip.metastore.ingenta.com/content/aip/journal/jcp/131/17/10.1063/1.3257681
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

REMPI of pyrrole. The resonant peaks are due to low-lying Rydberg states of pyrrole. These were the only features observed between (206 nm) and (390 nm).

Image of FIG. 2.
FIG. 2.

Repeated measurement of the REMPI spectrum of pyrrole in the region of the dominant peak at using (a) linear-polarized light and (b) circular-polarized light. The decrease in peak intensity in (b) is evidence that the excited intermediate is a Rydberg state.

Image of FIG. 3.
FIG. 3.

REMPI of 2,5-dimethylpyrrole. The vibronic structure is due to transitions into a potential well in the state. This band is the only feature observed between (206 nm) and (390 nm).

Image of FIG. 4.
FIG. 4.

TD-DFT (B3-LYP/def2-TZVP). The electronic energy of the state in pyrrole obtained at each step during the optimization of the molecular geometry has been plotted against the N–H internuclear distance, . The ground-state structure of pyrrole was used as a starting geometry in . All the nuclear coordinates were allowed to vary in the calculations, but showed the most significant changes. Single-point energies of the ground state and the excited states , , and have been calculated using the same molecular geometry obtained for .

Image of FIG. 5.
FIG. 5.

TD-DFT (B3-LYP/def2-TZVP). The electronic energy of (a) , (b) , (c) , and (d) states in pyrrole obtained at each step during the optimization of the molecular geometry, . The ground-state structure of pyrrole was used as the starting geometry in (a) and (c), and the minimum-energy structure at the and intersections was used as the starting geometries in (b) and (d), respectively. In (a) and (c), it is that undergoes the most significant change in length. However, in (b) and (d), there is a nonplanar deformation of pyrrole, which is not illustrated in the graphs.

Image of FIG. 6.
FIG. 6.

DFT and TD-DFT (B3-LYP/def2-TZVP). The molecular geometries in the ground state (DFT) and at the intersections between excited states (TD-DFT) in pyrrole. The electronic energy and N–H internuclear distance are displayed on the vertical and horizontal axes, respectively. Note that the molecule undergoes a nonplanar distortion at the intersection, and other coordinates than have an important role in the deactivation of photoexcited pyrrole.

Image of FIG. 7.
FIG. 7.

TD-DFT (B3-LYP/def2-TZVP). The full deactivation pathway from the photoexcited state in pyrrole through intersections with lower dissociative and states. The final fate of the excited molecules might be N–H bond fission (on ) or internal conversion (to ) followed by ring opening.

Image of FIG. 8.
FIG. 8.

TD-DFT (B3-LYP/various basis sets). A relaxed potential energy scan of the state with respect to the N–H internuclear distance using the Dunning aug-cc-pVDZ (dotted line), the def2-TZVP (dashed line), and the N-augmented def2-TZVP (solid blue line) basis sets. Ground-state energies are consistent between basis sets and are calculated at the geometries. Earlier MRCI calculations (Ref. 8) give the vertical-excitation energy to be 4.9 eV. The present TD-DFT calculations using the N-augmented def2-TZVP basis set give a value of 4.72 eV with a plateaux in the energy profile similar to that found in Ref. 8.

Image of FIG. 9.
FIG. 9.

TD-DFT (B3-LYP/N-augmented def2-TZVP). The molecular geometries in the ground and states of 2,5-dimethylpyrrole. The geometry in the excited state has symmetry.

Image of FIG. 10.
FIG. 10.

TD-DFT (B3-LYP/N-augmented def2-TZVP). Plot of the electron density in the state of 2,5-dimethylpyrrole. A -type orbital on the nitrogen and -type orbital on the attached hydrogen nuclei interact with the delocalized -system.

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/content/aip/journal/jcp/131/17/10.1063/1.3257681
2009-11-03
2014-04-24
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Comparison of the resonance-enhanced multiphoton ionization spectra of pyrrole and 2,5-dimethylpyrrole: Building toward an understanding of the electronic structure and photochemistry of porphyrins
http://aip.metastore.ingenta.com/content/aip/journal/jcp/131/17/10.1063/1.3257681
10.1063/1.3257681
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