The photodissociation dynamics of ozone at 193 nm: An O([sup 1]D[sub 2]) angular momentum polarization study (original) (raw)
2006, The Journal of Chemical Physics
Polarized laser photolysis, coupled with resonantly enhanced multiphoton ionization detection of O͑ 1 D 2 ͒ and velocity-map ion imaging, has been used to investigate the photodissociation dynamics of ozone at 193 nm. The use of multiple pump and probe laser polarization geometries and probe transitions has enabled a comprehensive characterization of the angular momentum polarization of the O͑ 1 D 2 ͒ photofragments, in addition to providing high-resolution information about their speed and angular distributions. Images obtained at the probe laser wavelength of around 205 nm indicate dissociation primarily via the Hartley band, involving absorption to, and diabatic dissociation on, the B 1 B 2 ͑3 1 A 1 ͒ potential energy surface. Rather different O͑ 1 D 2 ͒ speed and electronic angular momentum spatial distributions are observed at 193 nm, suggesting that the dominant excitation at these photon energies is to a state of different symmetry from that giving rise to the Hartley band and also indicating the participation of at least one other state in the dissociation process. Evidence for a contribution from absorption into the tail of the Hartley band at 193 nm is also presented. A particularly surprising result is the observation of nonzero, albeit small values for all three rank K =1 orientation moments of the angular momentum distribution. The polarization results obtained at 193 and 205 nm, together with those observed previously at longer wavelengths, are interpreted using an analysis of the long range quadrupole-quadrupole interaction between the O͑ 1 D 2 ͒ and O 2 ͑ 1 ⌬ g ͒ species.
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The photodissociation dynamics of O2 at 193 nm: an O(3PJ) angular momentum polarization study
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Polarized laser photolysis, coupled with resonantly enhanced multiphoton ionization detection of O͑ 1 D 2 ͒ and velocity-map ion imaging, has been used to investigate the photodissociation dynamics of ozone at 193 nm. The use of multiple pump and probe laser polarization geometries and probe transitions has enabled a comprehensive characterization of the angular momentum polarization of the O͑ 1 D 2 ͒ photofragments, in addition to providing high-resolution information about their speed and angular distributions. Images obtained at the probe laser wavelength of around 205 nm indicate dissociation primarily via the Hartley band, involving absorption to, and diabatic dissociation on, the B 1 B 2 ͑3 1 A 1 ͒ potential energy surface. Rather different O͑ 1 D 2 ͒ speed and electronic angular momentum spatial distributions are observed at 193 nm, suggesting that the dominant excitation at these photon energies is to a state of different symmetry from that giving rise to the Hartley band and also indicating the participation of at least one other state in the dissociation process. Evidence for a contribution from absorption into the tail of the Hartley band at 193 nm is also presented. A particularly surprising result is the observation of nonzero, albeit small values for all three rank K =1 orientation moments of the angular momentum distribution. The polarization results obtained at 193 and 205 nm, together with those observed previously at longer wavelengths, are interpreted using an analysis of the long range quadrupole-quadrupole interaction between the O͑ 1 D 2 ͒ and O 2 ͑ 1 ⌬ g ͒ species.
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The photodissociation of ozone has been studied at 193nm using high resolution photofragment translational spectroscopy. The results show 6 distinct peaks in the time-of-flight spectra for the 0 2 product and its momentummatched 0 atom counterpart. The translational energy distributions determined from the time-of-flight spectra reveal the production of a range of electronic states of the photofragments. The product electronic states were identified based on the translational energy distributions, with the aid of state-resolved imaging experiments by Houston and coworkers. The results reveal the production of a substantial yield of highly excited triplet states of 0 2 , recently suggested to play an important role in the stratospheric ozone balance. In addition, peaks corresponding to 0 2 (a 1~9) and 0 2 (b 1~d) were observed, the latter confirming a previous report [A. A. Turnipseed, et al., J. Chern. Phys. 95, 3244 (1991)]. Evidence was seen for a small contribution from the triple dissociation 0 3-+ 30(3 P), and insight into the dissociation dynamics for this process was inferred from the translational energy distributions. Branching fractions and angular distributions were measured for all channels. The latter were found in general to yield negative f3 parameters, in contrast to what is seen at longer wavelengths .
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