The photodissociation dynamics of ozone at 193nm: An O(D21) angular momentum polarization study

Abstract

Polarized laser photolysis, coupled with resonantly enhanced multiphoton ionization detection of O (1D 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 O (1D 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 1B2(3 1A l) potential energy surface. Rather different O (1D 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 O (1D 2) and O2(1Ag) species.

Photodissociation dynamics of OCS at 248nm: The S(D21) atomic angular momentum polarization

“…28 The experimentally acquired images can be written in the form of a Fourier series: 28 I͑r,⌽͒ = C 0 ͑r͒ + 2 ͚ nϾ0 C n ͑r͒cos n⌽ + CЈ n ͑r͒sin n⌽, ͑4͒ 28 The experimentally acquired images can be written in the form of a Fourier series: 28 I͑r,⌽͒ = C 0 ͑r͒ + 2 ͚ nϾ0 C n ͑r͒cos n⌽ + CЈ n ͑r͒sin n⌽, ͑4͒…”

“…In practice, the f K Ј ͑q , qЈ ; v͒ dynamical functions are usually recast in terms of a variety of different ͑but equivalent͒ factors, including the polarization parameters of Rakitzis and Zare 41 and the polarization anisotropy parameters of Vasyutinskii and co-workers. 28 The fitted coefficients for all polarization parameters from Eq. The best-fit coefficients a K ͑q , qЈ ; i͒ for a given number of Gaussians, i max = 30, were determined using a genetic algorithm which selected from a pool of parameters randomly generated within the constraints of the physically allowed values.…”

“…45 Interpretation of the polarization parameters in the case of larger systems 42,46 is more problematic and awaits a detailed theoretical treatment. 28,39 These molecular frame parameters are functions of velocity and angle between the recoil direction and the electric vector of the photolysis light. 28,39 These molecular frame parameters are functions of velocity and angle between the recoil direction and the electric vector of the photolysis light.…”

“…2D wave packet calculations employing the ab initio PESs described above revealed that the most intense feature of the speed distribution, corresponding to lower CO͑X 1 ⌺ + ͒ rotational excitation, could be modeled by adiabatic dissociation on the 2 1 AЈ͑ 1 ⌬͒ surface, with the 1 1 AЉ͑ 1 ⌺ − ͒ state contributing about 10%. III D a long-range interaction model, described in detail previously, [27][28][29] is used to help interpret the polarization data, and provide some support for the view that excitation to the 1 1 AЉ plays a relatively minor role. It was also found that the low velocity feature in the S͑ 1 D 2 ͒ distribution ͑arising from population of high-J CO states in the CO cofragment͒ could only be reproduced by allowing nonadiabatic coupling between the 1 1 AЈ and 2 1 AЈ PESs.…”

Lineshape analysis of stimulated Raman spectra of the near‐nozzle region of free jet expansions

“…Among them, highresolution spectroscopic techniques, such as visible absorption, [3] diode-laser infrared absorption, [4,5] Fourier transform infrared (FTIR) absorption spectroscopy, [6,7] Fourier transform microwave (FTMW) measurements, [8] resonance enhanced multiphoton ionization (REMPI), [9,10] cavity ring down spectroscopy, [11] or nonlinear Raman spectroscopies (stimulated Raman Spectroscopy (SRS), CARS, etc), [12,13] have been widely used to measure vibrationrotation spectra of molecules cooled in the expansion and for the analysis of phenomena naturally occurring, or externally induced, in free jets and supersonic beams, like nonequilibrium between the molecular degrees of freedom, [9,10] nucleation and clustering of the gas, [11,12] photodissociation and photon-induced reactions, [14,15] or interactions of molecules with fields. [16] In the spectra obtained from jets with techniques that have a great field depth, like infrared absorption, the measured intensity and the profile of the spectral lines are the result of an integration along the line of sight, containing information about the density, temperature, and velocity of the observed particles within the jet.…”