A Simple Equivalent Bond Orbital Model for the Rationalization of the C2s-Photoelectron Spectra of the Higher n-Alkanes, in Particular of Polyethylene
✍ Scribed by Edgar Heilbronner
- Publisher
- John Wiley and Sons
- Year
- 1977
- Tongue
- German
- Weight
- 486 KB
- Volume
- 60
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
The higher homologues of n-alkanes H(CH2),H with N > -13 yield photoelectron spectra in which the (&-bands merge to form a double humped, unresolved C2,-band system in the interval of I = 15 to 25 eV [l]. It is shown that with the help of an equivalent bond orbital model one can derive a closed formula, which gives the individual C2,-band positions IF= -.cj in function of N and j with sufficient accuracy, assuming the validity of Koopmans' approximation. The calculated I;" values o= 1 to N) folded with an appropriate shape function for the individual C2,-bands reproduce the observed Franck-Condon envelope of the C2,-band system within narrow limits of error. However, a comparison of the observed total width of the C2,-band system with the computed one, indicate that for large n-alkanes (N> -13), the simplification which consists of taking into account only the interaction matrix elements between vicinal bond orbitals [ 2 ] , is no longer a satisfactory one.
If the m = 3 N + 1 canonical valence shell orbitals q,(r= 1,2, ... m) of an alkane CNH2N+2, obtained from a semi-empirical or ab initio SCF calculation, are