Alkali metals, ground-state energies

The question about the existence and the stability of pure carbon chain polymers has been repeatedly discussed in many papers. These polymers are called carbynes and are believed to consist of alternating triple and single bonds (polyynes) rather than of non alternating double bonds (polycumulenes) because of the lower ground state energy of the former. Thus, vibrational spectra of such materials are characterized by a more or less expressed structure around 2000 cm which is typical for the triple bond. A very efficient way to obtain such triple bonded carbon polymers nses an internal electrochemical reduction of fluorinated polymers such as poly(tetrafluoroethylene) (PTFE) or poly(tetrafluoroethylene/hexafluoropropylene) (FEP) by alkali metal amalgam according to the reaction... 

Ground state The lowest allowed energy state of a species, 137 Group 1 metal. See Alkali metal Group 2 metal See Alkaline earth metal Group A vertical column of the periodic table, 31... 

Flame emission photometry is used mainly for the determination of alkali metals and some easily excited elements (Na, K, Li, Ca, etc.). This is related to the fact that the number of excited atoms in the flame decreases exponentially with increasing excitation energy. Moreover, at variance to AAS, where the sensitivity is directly proportional to the number of atoms in the ground state, the sensitivity of AES increases with an increasing number of atoms in the excited state. 

It is tempting to relate the thermodynamics of electron-transfer between metal atoms or ions and organic substrates directly to the relevant ionization potentials and electron affinities. These quantities certainly play a role in ET-thermo-dynamics but the dominant factor in inner sphere processes in which the product of electron transfer is an ion pair is the electrostatic interaction between the product ions. Model calculations on the reduction of ethylene by alkali metal atoms, for instance [69], showed that the energy difference between the M C2H4 ground state and the electron-transfer state can be... 

A long-range electron transfer is possible in this reaction, as in alkali metal atom reactions. However, the resulting electron-transfer complex Ba NO does not correlate to the ground-state products BaO which has the structure Ba +0. Moreover, the NOJ ion is stable and its dissociation into NO 4- 0 is endoergic. Hence the Ba "NOj complex may survive for many rotational periods despite the availability of a very exoergic reaction channel. This is expected to dissociate after the transfer of the second valence electron of barium, which is probably hindered by an energy barrier. 

State-specific reactions of excited alkali metal atoms have been encountered a number of times. We have mentioned already the K -I- H2 KH - - H reaction which is turned on by excitation of potassium to the 7s level (ca. 3.7 eV above the ground state), and not by the excitation to the 5d D level, although it is only 0.01 eV below the 7s level [155, 156]. Such a change in reactivity is, of course, linked to the different potential energy surface on which the reaction is promoted, but owing to the equivalent energy of the 7s S and 5d D levels the difference in reactivity is connected with orbital symmetry. 

Figure 1. Schematic diagram of the energies of the anion ground state (M S), the lowest covalent state (M-S ), ion-pair state (M S ) and cation ground state (M+S ) versus /j M = alkali metal atom S = solvent molecules). The ion-pair state is expected to correlate with the ground state of the solvated electron plus the solvated M+ ion in bulk fluids. The ground-state electronic character of the neutral cluster changes from covalent to ion-pair type at a certain critical size.

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