Formation of O(3P j) photofragments from the Hartley band photodissociation of ozone at 226 nm

Abstract

The photodissociation of ozone at 226 nm is studied for O3→O2(X3 Σ−g)+O(2p3Pj) by probing O(3Pj) atomic photofragments with a resonance-enhanced multiphoton ionization method. Angular and kinetic energy distributions are determined by measuring time-of-flight spectra as a function of the angle between the polarization vector of the dissociation laser and the detector axis. The Doppler width of O(3Pj) photofragments is also measured. The translational energy distribution is well represented by assuming the formation of vibrationally excited O2 molecules with an average vibrational quantum number of 12. The anisotropy parameter β for the angular distribution is found to be 0.7±0.1. The predissociation dynamics from the photoprepared O3(1B2) state to the repulsive potential surface is discussed.

Photodissociation of ozone at 193 nm by high-resolution photofragment translational spectroscopy

“…The fourth channel is assigned as highly vibrationally excited 0 2 (X 3 E_;) based on the following observations: A slow component in the recoil velocity distribution was previously reported for the triplet channel at 226 nm and found, based on direct probing of the nascent products in a cell experiment, to correspond to the production of highly vibrationally excited, ground electronic state 0 2 • [4,45] In addition, the P(Er) for this channel cuts off precisely at the threshold for triple dissociation, implying that it involves the formation of a ground state oxygen atom. Finally, a strong peak at the same energy was observed in the imaging of oe P) at 193 nm, confirming it as a triplet channel.…”

“…[44] Previous measurements in the Hartley band reveal positive j3 values that are substantially lower than this, ranging from j3 = 0. 7 (reported at 226 nm) [45] to 1.0 (for the singlet channel at 274 nm). [10] For My type transitions in the limit of prompt recoil these correspond to bond angles of 98° and 109°, respectively.…”

“…This identification is based on a number of observations: 1) the P(Er) obtained from both imaging [4] and Doppler [45] measurements of the oe P) fragment from 226 nm dissociation of ozone showed a similar broad, high energy component, shifted by the 15.0 kcal difference in available energy; 2) imaging results for the oe P) fragment at 193 nm [46] showed two peaks, one of which matched this one; and 3) the fastest peak obviously corresponds most likely to the production of ground electronic state products. The molecular product is probably in a broad range of excited vibrational levels, consistent with results reported elsewhere in the Hartley band.…”

“…The molecular product is probably in a broad range of excited vibrational levels, consistent with results reported elsewhere in the Hartley band. [4,47,45] If we assume a· rotationally impulsive dissociation, the fraction of available energy appearing in rotation is variously given in the range of 15 to 23%. [12,47] For the maximum of the peak, the translational energy release corresponds to 68 kcal/mol.…”

An evaluation of autocatalytic ozone production from vibrationally excited oxygen in the middle atmosphere

“…Kinugawa et al (1990) have deduced a vibrational distribution of the 02 fragment following ozone photolysis at 226 nm. This distribution was used in the study by Toumi et al (1991).…”