Common-image gathers are an important output of prestack depth migration. They provide information needed for velocity model building and amplitude and phase information for subsurface attribute interpretation. Conventionally, common-image gathers are computed using Kirchhoff migration on commonoffset/azimuth data volumes. When geologic structures are complex and strong contrasts exist in the velocity model, the complicated wave behaviors will create migration artifacts in the image gathers. As long as the gather output traces are indexed by any surface attribute, such as source location, receiver location, or surface plane-wave direction, they suffer from the migration artifacts caused by multiple raypaths. These problems have been addressed in a significant amount of work, resulting in common-image gathers computed in the reflection angle domain, whose traces are indexed by the subsurface reflection angle and/or the subsurface azimuth angle.Most of these efforts have concentrated on Kirchhoff and oneway wave-equation migration methods. For reverse time migration, subsurface angle gathers can be produced using the same approach as that used for one-way wave-equation migration. However, these approaches need to be revisited when producing high-quality subsurface angle gathers in three dimensions (reflection angle/azimuth angle), especially for wide-azimuth data. We have developed a method for obtaining 3D subsurface reflection angle/azimuth angle common-image gathers specifically for the amplitude-preserved reverse time migration. The method builds image gathers with a highdimensional convolution of wavefields in the wavenumber domain. We have found a windowed antileakage Fourier transform method that leads to an efficient and practical implementation. This approach has generated high-resolution angle-domain gathers on synthetic 2.5D data and 3D wideazimuth real data.

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Full three-dimensional time-dependent quantum wave-pack calculations have been carried out for the F+HCl and F+DCl reactions on a many-body expansion of the ground 2A′HClF potential energy surface. The calculated energy-dependence of reaction probability exhibits oscillating structure in the F+HCl reaction but not in the F+DCl system. The effects of initial state excitation on the total reaction probabilities as a function of collision energy are investigated for reactions from various initial vibrational and rotational states of HCl and DCl. Our results show that reagent vibrational and/or rotational excitation can generally lead to an increase in reaction probability at low collision energy and a slight decrease at relatively high collision energy. Thermal rate constants for the title reactions are calculated and they are in generally good agreement with experimental measurement. Investigation of steric effects for the reactions indicates that the H (or D) side of HCl (or DCl) molecule is only slightly favored for reactive attack and reaction proceeds from almost all attack angles. The present results indicate that the H/D kinetic isotope effect should not be totally neglected.