High resolution ion imaging study of BrCl photolysis in the wavelength range 330–570 nm

Speed dependent rotational angular momentum polarization of the O2 (aΔg1) fragment following ozone photolysis in the wavelength range 248–265nm

The translational anisotropy and rotational angular momentum polarization of a selection of rotational states of the O2 (a 1Deltag; v=0) photofragment formed from ozone photolysis at 248, 260, and 265 nm have been determined using the technique of resonance enhanced multiphoton ionization in combination with time of flight mass spectrometry. At 248 nm, the dissociation is well described as impulsive in nature with all rotational states exhibiting similarly large, near-limiting values for the bipolar moments describing their angular momentum alignment and orientation. At 265 nm, however, the angular momentum polarization parameters determined for consecutive odd and even rotational states exhibit clear differences. Studies at the intermediate wavelength of 260 nm strongly suggest that such a difference in the angular momentum polarization is speed dependent and this proposal is consistent with the angular momentum polarization parameters extracted and reported previously for longer photolysis wavelengths [G. Hancock et al., Phys. Chem. Chem. Phys. 5, 5386 (2003); S. J. Horrocks et al., J. Chem. Phys. 126, 044308 (2007)]. The alternation of angular momentum polarization for successive odd and even J states may be a consequence of the different mechanisms leading to the formation of the two O2 (a 1Deltag) Lambda doublets. Specifically, the involvement of out of plane parent rotational motion is proposed as the origin for the observed depolarization for the Delta- relative to the Delta+ state.

Velocity map imaging study of BrCl photodissociation at 467 nm: determination of all odd-rank (K = 1 and 3) anisotropy parameters for the Cl(2P(3/2)0) photofragments

Resonance-enhanced multiphoton ionization and velocity map imaging of the Cl(2P(3/2)0) fragments of BrCl photolysis at 467.16 nm have been used to obtain a complete set of orientation parameters (with ranks K = 1 and 3) describing the polarization of the electronic angular momentum. The experiments employ two geometries distinguished only by the circular or linear polarization of the photolysis laser beam. Normalized difference images constructed from the data accumulated using a right or left circularly polarized probe-laser beam, counterpropagating with the photolysis laser, were fitted to basis images corresponding to contributions from various odd-rank anisotropy parameters. Expressions are given for the difference images in terms of the K = 1 and 3 anisotropy parameters, which describe coherent and incoherent parallel and perpendicular excitation and dissociation mechanisms. The nonzero values of the anisotropy parameters are indicative of nonadiabatic dissociation dynamics, with likely contributions from flux on the A 3Pi1,B 3Pi(0+),C 1Pi1, and X 1sigma+(0+) states as well as one further omega = 1 state, all of which correlate adiabatically to Cl(2P(3/2)0) + Br(2P(3/2)0) photofragments. The magnitudes of the parameters depend both on the amplitudes of dissociative flux in these states, and also on the phases accumulated by the nuclear wave functions for different dissociation pathways.

Atomic polarization in the photodissociation of diatomic molecules

The angular momentum polarization of atomic photofragments provides a detailed insight into the dynamics of the photodissociation process. In this article, the origins of electronic angular momentum polarization are introduced and experimental and theoretical methods for the measurement or calculation of atomic orientation and alignment parameters described. Many diatomic photodissociation systems are surveyed, in order to provide an overview both of the historical development of the field and of the most state-of-the-art contemporary studies.

Imaging the dynamics of gas phase reactions

Ion imaging methods are making ever greater impact on studies of gas phase molecular reaction dynamics. This article traces the evolution of the technique, highlights some of the more important breakthroughs with regards to improving image resolution and in image processing and analysis methods, and then proceeds to illustrate some of the many applications to which the technique is now being applied--most notably in studies of molecular photodissociation and of bimolecular reaction dynamics.