Excited state characterisation of hydrogen halides using velocity map imaging

Methods of extracting dynamical information from velocity map imaging data are presented, from determination of photoproduct energies and spatial anisotropies to reconstruction of superexcited state potential energy curves for HI and HCl and modelling of the product angular distributions for dissociation of HCl and HBr.; First, two algorithms are presented that permit analysis of images obtained by velocity map imaging, and, more generally, of any Abel invertible image. One---the "onion peeling" algorithm---is based on the reconstruction of the 3D particle distribution while the other uses pattern recognition to deal with uneven distributions of intensity, background signals, and realistic distortions of circularity. The velocity profile, branching ratios, and spatial anisotropy parameters are calculated using an analytical description of the raw image and for any form of the velocity broadening function.; The reconstruction of potential energy curves of excited states from imaging data is performed using least-square fitting for HI/DI and HCl. For HI and DI, a comprehensive empirical analysis based on all available total absorption coefficients and branching ratio data for the UV photodissociation spectra was used to determine analytical forms for the potential energy curves of the four excited electronic states A 1pi1, a 3pi0+, a 3 pi1, and t 3Sigma 1+, and the associated transition moment functions. The analysis confirms that four final states are involved in the A-band absorption of HI and that those states dissociate adiabatically to form H + I* and H + I following parallel and perpendicular transitions, respectively.; In the case of HCl, from a potential fit to the intensities of the vibrationally resolved photoelectron spectrum of HCl+ we find that a single superexcited state acts as a gateway to autoionisation and dissociation into H + Cl*(4s) following excitation from the E state. It is most likely a repulsive and low-n Rydberg state with a ( 4pi) ion core.; Further, to model the H-atom photofragment angular distributions from single-photon dissociation of two-photon rovibronically state-selected HCl and HBr, a formalism for calculating the angular momentum polarisation following two-photon excitation of a J-selected state is developed. It is used to identify both the virtual state symmetry in the two-photon absorption and the symmetry of the dissociative state using light of linear polarisation only.