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Spectroscopic and computational studies of matrix-isolated iso-CHBr3: Structure, properties, and photochemistry of iso-bromoform
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Image of FIG. 1.
FIG. 1.

Photochemical pathways for bromoform in (a) the gas phase, (b) condensed phases. In condensed phases, geminate recombination in the solvent cage forms iso-CHBr3.

Image of FIG. 2.
FIG. 2.

Upper panel: Infrared spectrum of a CHBr3:Ne matrix (∼1:500) at ∼5 K following laser irradiation at 220 nm to form the iso-species, and subsequent irradiation at 440 nm to regenerate the parent. The stick spectrum shows the predicted (B3LYP/aug-cc-pVTZ) infrared spectrum of iso-CHBr3. Lower panel: The corresponding UV/VIS spectrum, compared with the predicted (TDCAM-B3LYP/aug-cc-pVTZ) spectrum of iso-CHBr3.

Image of FIG. 3.
FIG. 3.

Relaxed two-dimensional potential energy surface scan of iso-CHBr3 along ∠C–Br–Br and RBr–Br, calculated at the M06/6-311++G(2df,2p) level of theory. The atom labels refer to the numbering scheme in Figure 1(b).

Image of FIG. 4.
FIG. 4.

Calculated stationary points on the CHBr3 potential energy surface at the CCSD(T)//MP2/aug-cc-pVTZ level. See the text for details.

Image of FIG. 5.
FIG. 5.

Difference IR spectrum obtained following 440 nm laser irradiation of matrix isolated iso-CHBr3. The IR absorptions of the iso-species decrease, and the bands of the parent increase, illustrating a facile back photoisomerization. For reference, the spectrum of matrix isolated (Ar, 5 K) CHBr3 is shown in the upper panel.

Image of FIG. 6.
FIG. 6.

Intrinsic reaction coordinate scan (black circles, referenced to y axis at left) from the iso-CHBr3 transition state, calculated at the MP2/aug-cc-pVTZ level. Also shown, referenced to the y axis at right, are the relative weights of the four most important resonance structures, identified at right, along the IRC path. The resonance weights were calculated using natural resonance theory as described in the text.


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Table I.

Vibrational frequencies of iso-CHBr3 and its deuterated isotopomer.

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Table II.

Predicted (TDCAM-B3LYP/aug-cc-pVTZ) and observed electronic absorptions for iso-CHBr3.

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Table III.

Fully optimized geometrical parameters for CHBr3, iso-CHBr3, and the first-order saddle point connecting the two isomers. Angles are given in degrees and bond lengths in Ångstroms; atom numbering follows the scheme shown in Figure 1(b).


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Spectroscopic and computational studies of matrix-isolated iso-CHBr3: Structure, properties, and photochemistry of iso-bromoform