Application of time-sliced ion velocity imaging to crossed molecular beam experiments

Abstract

A three-dimensional (3D) ion velocity imaging method was developed to measure the product velocity distributions in crossed molecular beam experiments. While maintaining conventional two-dimension velocity mapping, the third velocity component was mapped linearly to the ion time of flight. A weak extraction field was used to spread the ion turnaround time to several hundred nanoseconds, which permits good resolution for selection of the longitudinal velocity. A fast gated (⩾5 ns) intensified charge coupled device camera was used to record time-sliced ion images. Calibration of the apparatus was done by measuring O+ images from the multiphoton dissociation/ionization of O2. The resolution in velocity achieved was about 1% (Δv/v) in slicing through the center of a Newton sphere. The overall performance was examined by observing product ion images from the F+CD4→DF+CD3 reaction. To detect CD3+ with kinetic energy release of about 1 eV, 50 ns time slicing provides sufficient velocity resolution, such that resolution of the image is mainly limited by the spread in velocity of the two molecular beams. These ion optics can focus on a large volume of ion cloud, which is crucial in crossed molecular beam experiments. Direct 3D imaging also simplifies data analysis. This direct 3D ion imaging method provides a powerful tool with which to study systems with no cylindrical symmetry.

Ultrafast Relaxation Dynamics Observed Through Time-Resolved Photoelectron Angular Distributions

“…It is also worth pointing out that the resistive glass tubes employed here may find uses in other VMI arrangements where a series of resistors have been used to generate smoothly varying fields. 25 The velocities of emitted photoelectrons (speed and angle) are projected onto the detector where the current is amplified by the MCPs. These are then accelerated to and impact on the phosphor screen from which emitted light is subsequently captured using a CCD camera (Basler, A312f).…”

Slice imaging of photodissociation of spatially oriented molecules

“…2 A special ion lens geometry was used to reduce the spatial blurring due to the extended size of the ion source. More recently, Kitsopoulos and co-workers, 3 Suits and co-workers, 4 and Liu and co-workers 5 demonstrated how a slice of the threedimensional ion cloud can be obtained by spreading the ion cloud in time. This latter method, called slice imaging, has the advantage that there are no restrictions with respect to cylindrical symmetry for analyzing the imaging data.…”

Communication: Imaging the effects of the antisymmetric-stretching excitation in the O(3P) + CH4(v3 = 1) reaction

“…Its angular distribution spans over a broad angular range-in sharp contrast to the backward dominance in the ground-state reaction. 17 After the density-to-flux transformation, 28,32 Figure 2 presents the desired product speed (left) and angular (right) distributions. In each panel the distributions of both stretchexcited (in red) and ground-state (in black) reactions are displayed for ready comparisons.…”

“…25 After the collisions, the ground state CH 3 (0 0 ) products were detected by a (2+1) resonance-enhanced multiphoton ionization (REMPI) method 26,27 and recorded by a time-sliced, velocity-imaging technique. 28 Due to the low S/N ratios, the probe laser wavelength was fixed at the peak of the Q-head; thus, mainly the low N-states of CH 3 (0 0 ) were sampled. To interrogate the effects of antisymmetric-stretching excitation, the product images at each E c were acquired alternatively with IR-on and IR-off.…”