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Ultraviolet photolysis of adenine: Dissociation via the state
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Image of FIG. 1.
FIG. 1.

Cuts through schematic singlet PESs of adenine based on CASPT2 (Ref. 29), MRCI-DFT (42), and TD-DFT (this work) calculations. Geometries are constrained except in the coordinate and therefore represent vertical excitation energies. potentials are shown as full lines and individually labeled, potentials are shown as dotted lines, and the potential is shown by a dot-dashed line. Triplet state potentials are not shown.

Image of FIG. 2.
FIG. 2.

Detail of the oven design, incorporating an extended poppet with Vespel tip.

Image of FIG. 3.
FIG. 3.

TKER spectra obtained from H atom TOF spectra recorded with at (a) , (b) , and (c) assuming .

Image of FIG. 4.
FIG. 4.

TKER spectra obtained from H atom TOF spectra recorded with at (a) , (b) , (c) , and (d) . Two spectra are shown in panel (c). (i), shown in black, as with the spectra displayed in panels (a), (b), and (d) was obtained with an unfocussed photolysis laser beam, whereas (ii), in gray, was obtained with a loosely focused ( fl) photolysis beam. (i) and (ii) have been scaled to have an equal intensity at TKER .

Image of FIG. 5.
FIG. 5.

TKER spectra obtained at with (b) 90° and (c) 0°. (a) shows the corresponding vs TKER plot.

Image of FIG. 6.
FIG. 6.

Expanded view of the calculated potentials for the (, , and ) states and the lowest state of adenine, plotted as a function of (with all other coordinates held fixed at their ground state equilibrium values). The gas phase absorption spectrum (solid black curve) (Ref. 9) is shown on the left, along with an illustrative simulation (solid gray curve) derived from CASPT2 calculated (Ref. 55) transition energies and oscillator strengths by convoluting appropriately weighted Gaussian contributions (dotted curves) for the first three excitations. Excitation at is assumed to populate both the and states (black dotted curves), which couple via their respective CIs to the PES and dissociate to adeninyl fragments. Our favored interpretation of the experimental data assumes that the disappearing out-of-plane wagging mode drives the coupling [a case (a) mode, indicated by the dotted effective potential], whereas coupling involves the out-of-plane mode , which maps into the level of the radical product [a case (b) spectator mode, illustrated by the continuous effective potential].

Image of FIG. 7.
FIG. 7.

and transition dipole moments in the tautomer of adenine returned by the present calculations (black), with angles relative to the ring-fusion axis (dotted) and to the bond (gray).


Generic image for table
Table I.

Internal energies (, in ) associated with peaks evident in one or more of the TKER spectra obtained in the wavelength range , with aligned at the listed angle relative to the detection axis, quoted relative to the peak at which is defined as having an associated . Plausible adeninyl product state assignments, as discussed in the text, are also listed. [ indicates the involvement of (disappearing) parent mode in driving population transfer through the CI].


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Ultraviolet photolysis of adenine: Dissociation via the π1σ* state