Ground State of CH

In terms of molecular orbital theory, the electronic ground state of CH has the following electron configuration ... 

Bernheim et al. (11). in examining the EPR spectra of CHg which was produced by the photolysis of diazlrlne and trapped in xenon at 4 K, concluded that the ground state of CH is a triplet state and it is bent. In similar followup work, they deduced... 

Fig. 5. Comparison of spin-coupled VB (0 500 structures ) and MCSCF-CI calculations ( Green et al. ) for the ground state of CH. ...

The first study on accidental three-state conical intersections was done for the CH cation by Katriel and Davidson. In a tetrahedral geometry, the ground state of CH is a T2 state. Therefore, it is triply degenerate as required by symmetry. Only one degree of freedom exists that will preserve Tj symmetry, and the dimensionality of the seam is one because all the requirements for degeneracy are satisfied by symmetry. The authors found additional three-fold degeneracies in this system even when the tetrahedral symmetry was broken. If no symmetry is present, the cation has 9 degrees of freedom and the dimensionality of the seam becomes 9 — 5 = 4. 

Different aromatic hydrocarbons (naphthalene, pyrene and some others) can form excimers, and these reactions are accompanying by an appearance of the second emission band shifted to the red-edge of the spectrum. Pyrene in cyclohexane (CH) at small concentrations 10-5-10-4 M has structured vibronic emission band near 430 nm. With the growth of concentration, the second smooth fluorescence band appears near 480 nm, and the intensity of this band increases with the pyrene concentration. At high pyrene concentration of 10 2 M, this band belonging to excimers dominates in the spectrum. After the act of emission, excimers disintegrate into two molecules as the ground state of such complex is unstable. 

The optimized geometries of (4.55a)-(4.55d) are shown in Fig. 4.17 and selected geometrical parameters are summarized in Table 4.13. The molecular shapes and NBO descriptors (not presented) generally agree with the idealized Lewis-like sd/x picture for Os(CH2)2, HW(CH2)(CH), and W(CH2)3. However, theC—W—C angle (42°) in the ground state of W(CH)2 is much smaller than expected for idealized sd1 geometry, and the optimal NBO description corresponds to a metallacyclopropene,... 

From the preceding calculation we see that the hypothetical ion pair for ethane lies about 57 kcal. above the energy of two adjacent methyl free radicals. While this is large it still permits us to consider that the ground state of two adjacent CHs may contain a small amount of partial ionic character. If we had made our calculation for a separation of 2.0 A. between the two C atoms of the methyl groupsf then Qc would... 

From our discussion on the CHs-CH3 ion pair, we would expect that the C2H4 biradical ion pair with a distance of only 1.54 A. between C atoms would be even more stable. If such a model is correct it would imply that there is a considerable amount of ionic character even in the ground states of double bonds, f... 

Table 3 Computed167 and experimental spectroscopic constants for the ground and various excited states of CH°...

Table 10.19. Spin-orbital single configuration representations for the ground and lowest excited electronic states of CH. Only the spatial and spin coordinates of the three highest-energy electrons are specified...

Hirata [54] has made some extended basis set studies on excited states of the CH radical and formaldehyde. He obtained Te values and dipole moments for the ground state and 4 excited states of CH with the CCSD, CCSDT, and CCSDTQ... 

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