A convenient switch design for high time resolution and energy resolution in ion velocity imaging

Time-sliced velocity map imaging (VMI) has extensively been applied in photodissociation dynamics studies, thanks to its unique advantages, such as high energy resolution and no requirement of inverse Abel or Hankel transformations. However, its time resolution is generally insufficient for distinguishing adjacent m/z ions with a certain kinetic energy due to the overlapping of time-of-flight distributions. Herein, we have made a novel and convenient switch design for the common ion optics in three-dimensional (3D) VMI. By simply introducing two additional resistors out of the vacuum chamber, the strength ratio of the extraction and acceleration fields is easily changed from 3D VMI to two-dimensional (2D) VMI under optimized conditions, as well as a significant extension of free drift length, leading to a higher time resolution while maintaining the high energy resolution. As a result, 2D and 3D VMI can be quickly switched without breaking the vacuum and replacing the electrostatic plates.