Stark velocity filter for nonlinear polar molecules

A Stark velocity filter with a pulse nozzle was applied to ND(3), NH(3), CH(3)I, H(2)CO, C(6)H(5)CN and C(6)H(5)Cl at room temperature. The results demonstrate that the Stark velocity filter works successfully for any kind of nonlinear polar molecule. The number of molecules detected after the filter was approximately 10(7) per pulse with 0.5 ms duration time. The slowest component observed had a velocity corresponding to a few K. The velocity distributions observed were compared to the simulation based on the Stark effect on rotational states. It was found that the nature of the rotational energy level structure is important for predicting the velocity distribution. For heavier asymmetric top molecules, it was found that many avoided crossings due to the second-order interactions make it difficult to treat low-field seeking states properly in the simulation. Simulations show that the combination of He buffer gas pre-cooling and the Stark velocity filter works extremely effectively.