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Single and double photoionizations of methanal (formaldehyde)
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Image of FIG. 1.
FIG. 1.

The photoelectron spectrum of formaldehyde at 48.37 eV photon energy (lower curve): the small peaks near 9 and 13 eV are artifacts. The upper curve shows the distribution of energies of electrons ejected as pairs in double ionization under the same conditions.

Image of FIG. 2.
FIG. 2.

Complete double photoionization spectra of formaldehyde at 48.37 eV photon energy (25.6 nm) and 40.81 eV photon energy (30.4 nm). The dominance of band 1 is due to an inner-valence Auger effect, as explained in the text.

Image of FIG. 3.
FIG. 3.

Two-dimensional electron pair energy distribution maps for double photoionization of formaldehyde at the indicated photon energies. The vertical scales show ionization energy (photon energy minus electron energy sum), while the horizontal axes show the lower of the two electron energies.

Image of FIG. 4.
FIG. 4.

Spectra of from mainly direct double photoionization (lower curve) and mainly indirect double ionization (upper curve). The direct spectrum is extracted from the full electron pair distribution at 48.37 eV by choosing electron pairs of near equal energy. For the indirect spectrum, pairs where one electron has an energy below 0.25 eV are chosen, emphasizing both the inner-shell Auger process and the possibly distinct process giving very low-energy electrons, visible in Fig. 3.

Image of FIG. 5.
FIG. 5.

Definition of the internal coordinates of .

Image of FIG. 6.
FIG. 6.

MRCI potential-energy curves of the singlet (upper trace) and the triplet (lower trace) states of along the CH coordinate. The other internal coordinates were kept fixed at their equilibrium values in . The thick vertical solid line corresponds to the center of the Franck-Condon region defined as the maximum of the squared ground-state wave function of .

Image of FIG. 7.
FIG. 7.

CASSCF electronic density difference for the equilibrium geometry of the dication (see Table I). The step between the contours is . The full lines correspond to and the dashed lines to .

Image of FIG. 8.
FIG. 8.

Two-dimensional cuts of the 6-D MRCI potential-energy function of for all eight permutations of internal coordinates. The remaining coordinates in each cut are fixed at their equilibrium values in . The contour intervals are except for the cut along the and coordinates, for which the step between the contours is . The lowest energy at ( for the cut along and ) corresponds to the first contour inside.


Generic image for table
Table I.

Optimized equilibrium geometries, adiabatic excitation energies , vertical excitation energies , and dominant electronic configurations of the excited states of calculated at the cc-pV5Z/MRCI level of theory.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Single and double photoionizations of methanal (formaldehyde)