Ionic Geometries Research Articles

Validity of Franck—Condon analysis procedures for deduction of excited state and ionic geometries I. The X2Π and A2Σ + states of N 2O

Three Franck—Condon analysis procedures, namely the generating function method, the method of Coon et al. and the Duschinsky matrix method were applied to vibrational fine structures observed in the photoelectron bands of N 2O. The ionic geometries thus deduced for the X 2Π and A 2Σ + states of N 2O are in good agreement with experimental data. Criteria for the determination of signs for changes in bond lengths have been studied. Furthermore, the Duschinsky effect on vibrational intensity distributions accompanying electronic transitions are discussed in detail.

Validity of Franck—Condon analysis procedures for deduction of excited-state and ionic geometries: Part II. The X2B1 and A2A1 states of hydrogen oxide and hydrogen sulphur

The vibrational intensity distributions observed in the first two photoelectron bands of H 2O, D 2O and H 2S were adopted in studying the validity and limitations of different methods for carrying out Franck—Condon analyses. These methods include the generating function method, Coon et al.'s method, the Duschinsky matrix method and the two approximate methods involving the use of the vibrational quantum number with the maximum intensity as well as vertical and adiabatic ionization potentials within a progression. The geometries thus deduced for the H 2O + and H 2S + ions in the X 2 B 1 and A 2 A 1 states are in good agreement with observed values. Various criteria for the prediction of signs for changes in bond lengths and bond angles were discussed. Furthermore, the Badger's rule and the electrostatic force model were utilized to estimate quantitatively the changes in bond length on ionization.

Molecular parameters of excited molecules and ions—III. Geometries of dihaloethylenes in some ionic states

The vibrational fine structures of the photoelectron bands of gem-, cis- and trans-dihaloethylenes were used in Franck—Condon factor calculations leading to the deduction of ionic geometries of these molecules. Separability of electronic and nuclear motion, constancy of electronic transition moment and photoionization cross section within vibrational progressions, as well as the harmonic oscillator treatment, were assumed to be valid in the calculations. In the determination of the signs of the changes in bond lengths and bond angles of the molecules upon ionization, different criteria were utilized with the inclusion of the nodal repulsive force model for bond angle changes. Moreover, the two mechanisms, namely, the change in bond order and the change in electrostatic interaction as proposed by Coulson and Luz were investigated and were found to be important in geometric changes upon ionization.