Singlet ground state

Most stable polyatomic molecules whose absorption intensities are easily studied have filled-shell, totally synuuetric, singlet ground states. For absorption spectra starting from the ground state the electronic selection rules become simple transitions are allowed to excited singlet states having synuuetries the same as one of the coordinate axes, v, y or z. Other transitions should be relatively weak. 

If all spins ( 1/2) in an atom or molecule are paired (equal numbers of spin +1/2 and -1/2), the total spin must be zero, and that state is described as a singlet (total spin, S = 0 and the state is described by the term 2S + 1 = 1). When a singlet ground-state atom or molecule absorbs a photon, a valence electron of spin 1/2 moves to a higher energy level but maintains the same... 

Fig. 1. Relaxation of molecule-medium system subsequent to photoexcitation where Sq is the singlet ground state the fkst excited singlet state and...

Using these molecular states, the weak absorption observed between 490 and 640 nm for Cbo in solution (Fig. 6) [67] is assigned to transitions between the singlet ground state So and the lowest excited singlet state 5i (associated with the tiu orbital and activated by vibronic coupling). 

Structure inverts the ordering of the U2u LUMO and HOMOs thereby affording a singlet ground state (Fig. 4.7) and, at the same time, allowing the development of cross-ring S S bonding. 

In the case of the hydrogen molecule-ion H2" ", we defined certain integrals Saa, Taa, Tab, Labra- The electronic part of the energy appropriate to the Heitler-London (singlet) ground-state wavefunction, after doing the integrations... 

Steady-state kinetics. The cycloaddition reaction between the singlet ground state of 2-isopropylidene cyclopentane-1,3-diyl ( = S ) with acrylonitrile (A) is believed to occur by way of a biradical intermediate (BR),17... 

The poor data on PuF6 are probably best interpreted as a very small TIP of about 150 x 10-6 emu indicating a singlet ground state and a large crystal field splitting of the octahedral compound ( 5). 

If we apply the Mulak model of a pseudoaxial, D, symmetry (14), using a ratio c/a = 0.95, we find indeed a singlet ground state 0> and a first excited state 1> causing the observed TIP. Deviation from Di symmetry will affect to first order only the excited degenerate states and will not alter this simple... 

A few nitrenes have been shown to have singlet ground states. See Sigman, M.E. Autrey, T. Schuster, G.B. J. Am. Chem. Soc., 1988, 110, 4297. 

In other words, we estimate the spectrum of the AF-singlet ground state by applying a shift, to the calculated undectet spectmm. For this case we use an empirical shift of 13500 cm so as to yield maximum coincidence between the calculated and observed spectra, a value easily obtained, for example, if we had used the Slater-Condon integrals from the Fe ion in equation (1) rather than the values for neutral Fe. 

Like TME, the diradical 15 was shown to have nearly degenerate singlet and triplet states by magnetic susceptibility [60, 61], although the early works by Dowd identified a triplet ground state on the basis of ESR spectrum [62, 63], The UCCSD(T) calculations predicted a singlet ground state with a small S-T gap of... 

Singlet ground state was characterized by NMR, IR, UV spectroscopy and single-crystal X-ray [162]... 

Bicyclic 1,3-a-diradicals (60) prefer singlet ground states with significant S-T gaps. The kinetic stability of such singlet diradicals is also outstanding in all the smdied diradicals. 

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