Photoelectron spectra and molecular properties. 30, Pi-interactions in H3Si- and H3C-substituted acetylenes

The photoelectron (pe) spectra of mono- and disubstituted silyl- and methylacetylenes are assigned by comparison with the corresponding ionization potentials of acetylene, disilane, and ethane. The observed π splittings can be rationalized within a parameterized hyperconjugation model. Calculations using a modified CND0/2 procedure with and without inclusion of 3d orbitals in the basis set demonstrate that the usual parameters tend to overemphasize p,d, back-bonding. To rationalize available experimental data, 3d si orbitals need not to be considered explicitly-neither for the different dipole moments of methyl- and silylacetylenes nor for the general pe spectroscopic pattern of silicon compounds, i.e., high first ionization potential, reduced spin-orbit coupling, or band broadening

Photoelectron spectra of group 5 compounds. 2, Conformational analysis of diphosphine (P2H4)

The photoelectron spectra of certain hydrazines, disulfides, peroxides, and aminophosphines have been assigned to a unique conformer, being present under normal PE spectroscopic conditions. In contrast, different rotamers could be detected in the PE spectra of hexahydropyridazines and tetrasubstituted diphosphines and diarsines and were assumed for polysilanes. The composition of the rotameric mixture (transgauche) obtained for tetramethyldiphosphine from the relative PE peak areas had to be revised