High-resolution pulsed-field-ionization zero-kinetic-energy photoelectron spectroscopic study of the two lowest electronic states of the ozone cation O3+

Abstract

The pulsed-field-ionization zero-kinetic-energy ͑PFI-ZEKE͒ photoelectron spectrum of jet-cooled O 3 has been recorded in the range 101 000-104 000 cm Ϫ1 . The origins of the X 1 A 1 →X ϩ 2 A 1 and X 1 A 1 →à ϩ 2 B 2 transitions could be determined from the rotational structure of the bands, the photoionization selection rules, the photoionization efficiency curve, and comparison with ab initio calculations. The first adiabatic ionization energy of O 3 was measured to be 101 020.5(5) cm Ϫ1 ͓12.524 95͑6͒ eV͔ and the energy difference between the X ϩ 2 A 1 (0,0,0) and à ϩ 2 B 2 (0,0,0) states was determined to be ⌬T 0 ϭ1089.7(4) cm Ϫ1 . Whereas the X →X ϩ band consists of an intense and regular progression in the bending ( 2 ) mode observed up to v 2 ϩ ϭ4, only the origin of the X →à ϩ band was observed. The analysis of the rotational structure in each band led to the derivation of the r 0 structure of O 3 ϩ in the X ϩ ͓C 2v ,r 0 ϭ1.25(2) Å,␣ 0 ϭ131.5(9)°͔ and à ϩ ͓C 2v ,r 0 ϭ1.37(5) Å,␣ 0 ϭ111.3(38)°͔ states. The appearance of the spectrum, which is regular up to 102 300 cm Ϫ1 , changes abruptly at Ϸ102 500 cm Ϫ1 , a position above which the spectral density increases markedly and the rotational structure of the bands collapses. On the basis of ab initio calculations, this behavior is attributed to the onset of large-amplitude motions spreading through several local minima all the way to large internuclear distances. The ab initio calculations are consistent with earlier results in predicting a seam of conical intersections between the X ϩ and à ϩ states Ϸ2600 cm Ϫ1 above the cationic ground state and demonstrate the existence of potential minima at large internuclear distances that are connected to the main minima of the X ϩ and à ϩ states through low-lying barriers.

Rovibronic photoionization dynamics of asymmetric-top molecules

“…However, the resolution achieved in these investigations was not sufficient in order to determine whether the ground state is the 2 A 1 or the 2 B 2 component. The experimental confirmation of the theoretical prediction that theX + state is of 2 A 1 electronic symmetry [101][102][103] has only been achieved recently by the analysis of the rotational structure of the high-resolution PFI-ZEKE photoelectron spectrum which also showed that the origins of theX + andà + states are only separated by 1089.7 cm −1 [41]. This confirmation was performed on the basis of symmetry assignments and of simulations of the bands using the orbital ionization model.…”

“…Fig. 2 shows a schematic representation of the relevant molecular orbitals of O 3 together with the most important configurations contributing to theX 1 A 1 ,X + 2 A 1 andà + 2 B 2 states as predicted by theory [98,41]. Because of configuration interaction, theX + state of O + 3 is not formed by ionization out of the HOMO, the 1a 2 orbital.…”

“…Partially resolved rotational contours have been analyzed in the photoelectron spectra of larger asymmetric tops such as, for instance, fluorobenzene [35] and n-butylbenzene [36]. The recent improvement of the resolution of PFI-ZEKE photoelectron spectroscopy to better than 0.1 cm −1 [19] enabled the observation of the rovibronic structure in the spectra of a wider range of asymmetric tops such as CH 2 CO [37,38], C 2 H 4 [39,40] and O 3 [41].…”

Rotational state effect and fragmentation of small polyatomic molecular ions

“…The validity of the suggestion is seen from figure 2. It seems , is 0.6 eV [24]. It is likely that the likelihood of the bond rupture increases with the weakness of the bond.…”

Radical-mediated adsorption: Ozone oxidation of passivated silicon

“…The degree of biradical character varies inversely with the singlet-triplet energy splitting, which in ozone is rather large. Note that recent ab initio configuration interaction calculations [12] have shown that the electronic structure of ozone is dominated by a single determinant, arguing against a significant biradical character and explaining why DFT captures the structure and energetics of ozone well.…”