Isotopic and vibronic coupling effects in the valence electron spectra of H2 16O, H2 18O, and D2 16O

Abstract

Isotopic shift data for Hei induced high resolution valence electron spectra of H2 16O, H2 18O, and D2 16O are presented. From the differences in the vibrational subspectra we were able to deduce adiabatic ionization energies and geometries of the ions and to assign the excited vibrations to normal modes. The ν2 progression in the 2A1 band was found to be affected by strong vibronic coupling.

Excited states of the water molecule: Analysis of the valence and Rydberg character

“…Experimental data show a large energy difference ͑ϳ0.8 eV͒ between the vertical and adiabatic ionization energies, suggesting therefore an important geometrical molecular reorganization upon ionization, an effect which is consistent with a linear or quasilinear geometry for the 1 2 A 1 state. 50 As determined from the band maximum, the second vertical ionization energy is 14.7 eV, 50 matching the present computed value. According to the experimental ionization potentials, 50 the 1b 2 orbital is energetically well separated ͑Ͼ3 eV͒ from the two highest occupied MOs.…”

“…This assignment is consistent with the vibrational structure of the lowest-energy band of the photoelectron spectrum. 50 The 0-0 feature is the most intense transition of the band, indicating a similar geometry for the neutral molecule and the cation, as could be expected from ionization involving a nonbonding electron. Accordingly, the 1 2 B 1 state has been computed at the CASPT2 level ͑valence active space͒ to lie vertically at 12.54 eV above the ground state, in agreement with both the 0-0 band position recorded at 12.61 eV ͑Ref.…”

“…The shape of the corresponding potential energy curves is similar to the ground-state curve, as could be expected for Rydberg states converging to the 2 B 1 cationic state which has a geometry close to the ground-state one. 50 As can be seen in Fig. 1, the situation is clearly different for the 1 1 B 1 state.…”

“…4 ,11,12,14,16 The nature of the 1 1 B 1 state needs, however, further consideration. The band is broad, covering the energy range 6.8-8.2 eV, and has a poorly defined progression which has been related to the symmetric bending mode 4,11 or to the symmetric stretching vibration on the basis of the results reported by Makochenkawa et al 54 Comparison with the lowest-energy band of the photoelectron spectrum, 50 corresponding to the removal of a 1b 1 electron, showed that both bands have different shapes, suggesting therefore some valence character for the 1 1 B 1 state, according to Robin. 14 On the contrary, a more detailed analysis of the band at 7.4 eV performed by Wang et al 11 led these authors to propose a dominant valence nature for the 1 1 B 1 state.…”

Single photon ionization of van der Waals clusters with a soft x-ray laser: (SO2)n and (SO2)n(H2O)m

“…5 34 can function as the ionized molecular species in the cluster. Following ionization the charge can remain in either moiety and transfer between the two.…”