Cryogenic buffer-gas beams are a promising method for producing bright sources of cold molecular radicals for cold collision and chemical reaction experiments. In order to use these beams in studies of reactions with controlled collision energies, or in trapping experiments, one needs a method of controlling the forward velocity of the beam. A Stark decelerator can be an effective tool for controlling the mean speed of molecules produced by supersonic jets, but efficient deceleration of buffer-gas beams presents new challenges due to longer pulse lengths. Traveling-wave decelerators are uniquely suited to meet these challenges because of their ability to confine molecules in three dimensions during deceleration and their versatility afforded by the analog control of the electrodes. We have created ground state CH(X 2 Π) radicals in a cryogenic buffer-gas cell with the potential to produce a cold molecular beam of 10 11 mol./pulse. We present a general protocol for Stark deceleration of beams with a large position and velocity spread for use with a traveling-wave decelerator. Our method involves confining molecules transversely with a hexapole for an optimized distance before deceleration. This rotates the phase-space distribution of the molecular packet so that the packet is matched to the time varying phase-space acceptance of the decelerator. We demonstrate with simulations that this method can decelerate a significant fraction of the molecules in successive wells of a traveling-wave decelerator to produce energy-tuned beams for cold and controlled molecule experiments.
We demonstrate a time-of-flight electron energy analyzer that operates at an 80MHz repetition rate. The analyzer yields an energy resolution of 40meV for 3eV electrons. The energy resolution limit is dominated by the detector time (or temporal) resolution. With a currently available detector with a temporal resolution of 100ps, we predict an energy resolution of less than 1meV for 200meV electrons. This makes high repetition rate time-of-flight energy analyzers a promising low-technology alternative to current state-of-the-art techniques.
a b s t r a c tCold, velocity-controlled molecular beams consisting of a single quantum state are a powerful tool for exploring molecular interactions. Here, we explore the state purity and resulting dynamics of a Starkdecelerated beam of ammonia molecules where numerous rotational states are initially populated. Under these circumstances, Stark deceleration is shown to be ineffective at producing a molecular beam consisting of a single quantum state. Therefore, quantum state purity must be carefully considered when using Stark decelerated beams and analogous techniques, particularly in collision experiments where contributions from all quantum states must be addressed.
Cryogenic buffer-gas beam sources are capable of producing intense beams of a wide variety of molecules, and have a number of advantages over traditional supersonic expansion sources. In this work, we report on a neon matrix isolation study of carbon clusters produced with a cryogenic buffer-gas beam source. Carbon clusters created by laser ablation of graphite are trapped in a neon matrix and detected with a Fourier transform infrared spectrometer in the spectral range 4000 − 1000 cm −1 . Through a study of carbon cluster production as a function of various system parameters, we characterize the behavior of the buffer-gas beam source and find that approximately 10 11 − 10 12 of each cluster is produced with each pulse of the ablation laser. These measurements demonstrate the usefulness of cryogenic buffer-gas beam sources for producing molecular beams of clusters.
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