Valence photoionization and resonant core excitation of ozone – experimental and theoretical study of the C̃-state of O3+

Toward the observation of quartet states of the ozone radical cation: insights from coupled cluster theory

Since the discovery of ozone depletion, the doublet electronic states of the ozone radical cation have received much attention in experimental and theoretical investigations, while the low-lying quartet states have not. In the present research, viable pathways to the quartet states from the lowest three triplet states of ozone, (3)A(2), (3)B(2), and (3)B(1), and excitations from the (2)A(1) and (2)B(2) states of the ozone radical cation have been studied in detail. The potential energy surfaces, structural optimizations, and vibrational frequencies for several states of ozone and its radical cation have been thoroughly investigated using the complete active space self-consistent field, unrestricted coupled cluster theory from a restricted open-shell Hartree-Fock reference including all single and double excitations (UCCSD), UCCSD method with the effects of connected triple excitations included perturbatively, and unrestricted coupled cluster including all single, double, and triple excitations with the effects of connected quadruple excitations included perturbatively. These methods used Dunning's correlation-consistent polarized core-valence basis sets, cc-pCVXZ (X = D, T, Q, and 5). The most feasible pathways (symmetry and spin allowed transitions) to the quartet states are (4)A(1)<--(3)A(2), (4)A(2)<--(3)A(2), (4)A(1)<--(3)B(2), (4)A(2)<--(3)B(1), (4)B(2)<--(3)B(1), (4)A(2)<--(1)A(1), (4)B(2)<--(1)A(1), and (4)A(1)<--(1)A(1) with vertical ionization potentials of 12.46, 12.85, 12.82, 12.46, 12.65, 13.43, 13.93, and 14.90 eV, respectively.

Threshold photoelectron spectroscopy of ozone

Threshold photoelectron spectrum of ozone is presented for the first time at a resolution of 21-38 meV using synchrotron radiation in the energy region of 12-21 eV. The ionization energies of the first ionized states were determined and an interpretation of the O3 spectrum with respect to its first three ionic states, 1 2A1, 1 2B2, and 1 2A2, is presented. Above 16 eV the enhancement of the intensities of the 2 2B1, 3 2A1, and 4 2B2 band systems due to the contribution of indirect processes was observed, not accessible by conventional photoelectron spectroscopy. It was also resolved and assigned the extensive vibrational structures of ozone. Between 15.5 and 18.5 eV the main band contours are similar to those found in conventional photoelectron spectroscopy, except that our threshold photoelectron spectrum reveals extensive additional vibrational structures. The band 2 2B1 was found to present an irregular vibrational spacing DeltaE, with a minimum value of 80 meV at approximately 16.47 eV.

Core excitation in O3 localized to one of two symmetry-equivalent chemical bonds: molecular alignment through vibronic coupling

Core excitation from terminal oxygen OT in O3 is shown to be an excitation from a localized core orbital to a localized valence orbital. The valence orbital is localized to one of the two equivalent chemical bonds. We experimentally demonstrate this with the Auger-Doppler effect which is observable when O3 is core excited to the highly dissociative OT1s(-1)7a1 1 state. Auger electrons emitted from the atomic oxygen fragment carry information about the molecular orientation relative to the electromagnetic-field vector at the moment of excitation. The data together with analytical functions for the electron-peak profiles give clear evidence that the preferred molecular orientation for excitation only depends on the orientation of one bond, not on the total molecular orientation. The localization of the valence orbital "7a1" is caused by mixing of the valence orbital "5b2" through vibronic coupling of antisymmetric stretching mode with b2 symmetry. To the best of our knowledge, it is the first discussion of the localization of a core excitation of O3. This result explains the success of the widely used assumption of localized core excitation in adsorbates and large molecules.