The photodissociation dynamics of ozone at 226 and 248nm: O(PJ3) atomic angular momentum polarization

Abstract

Speed distributions, and spatial anisotropy and atomic angular momentum polarization parameters have been determined for the O((3)P(J)) products following the photodissociation of ozone at 248 and 226 nm using velocity map ion imaging. The data have been interpreted in terms of two dissociation mechanisms that give rise to fast and slow products. In both cases, excitation is believed to occur to the B state. Consistent with previous interpretations, the speed distributions, translational anisotropy parameters, and angular momentum polarization moments support the assignment of the major pathway to curve crossing from the B to the repulsive R surface, generating fast fragments in a wide range of vibrational states. For the slow fragments, it is proposed that following excitation to the B state, the system crosses onto the A state. The crossing seam is only accessible to molecules that are highly vibrationally excited and therefore possess modest recoil speeds. Once on the A state, the wavepacket is thought to funnel through a conical intersection to the ground state. The velocity distributions, spatial anisotropy parameters, spin-orbit populations and polarization data each lend support to this mechanism.

Photodissociation of ozone in the Hartley band: Potential energy surfaces, nonadiabatic couplings, and singlet/triplet branching ratio

“…We conclude that the dissociation mechanism suggested in Ref. 49 is unable to explain the very slow O͑ 3 P͒ products in the triplet channel.…”

“…The coupling between states A and X is relevant for the dissociation path B → A → X suggested by Brouard et al 49 for explaining the very slow O͑ 3 P͒ products in the triplet channel. The A/X coupling is also important for the creation of cyclic ozone, for example, by isomerization from the C 2v to the D 3h well employing tailored laser pulses as put forward by Artamonov et al 50 and Kurosaki et al 51 Calculations using only the lowest adiabatic PES are unrealistic.…”

“…That observation led them to the suggestion that these slow products are created by dissociation via the ground state X rather than the repulsive state R; according to the work of Rosmus et al 68 and Tashiro and Schinke 69 the ground state of ozone adiabatically correlates with O͑ 3 P 2 ͒ while the R-state connects with O͑ 3 P 0 ͒. Brouard et al 49 therefore proposed a dissociation mechanism for the production of the very slow products consisting of the following steps: ͑a͒ excitation of the B-state, ͑b͒ transition to the A-state, ͑c͒ nuclear motion into the region of cyclic ozone, ͑d͒ transition to the X-state near the A/X crossing seam, and ͑e͒ final dissociation on the lowest PES. This appealing scenario motivated the present study.…”

“…Brouard et al 49 measured the distribution of spin-orbit states for the very slow products in channel ͑1͒ and found it to be markedly nonstatistical, with the lowest state 3 P 2 of the O atom being preferentially produced. That observation led them to the suggestion that these slow products are created by dissociation via the ground state X rather than the repulsive state R; according to the work of Rosmus et al 68 and Tashiro and Schinke 69 the ground state of ozone adiabatically correlates with O͑ 3 P 2 ͒ while the R-state connects with O͑ 3 P 0 ͒.…”

“…14 49 More detailed discussions of the absorption spectrum, especially the role of thermal broadening, and the product energy distributions both in the singlet and the triplet channels will be published in forthcoming articles.…”